Plain and simply wrong. Fare class is only required for SDC on an economy class ticket. Availability in the front cabin is all that's required on a first/business class ticket.

Routing changes are allowed, provided the new routing is allowed under the fare rules. While we don't know OP's exact fare basis, BWI-DTW-ATL-YUL is commonly allowed under BWI-YUL fares.

Alright, I spoke to a second agent who said that a routing change counts as a voluntary change and not an SDC.

However, [MENTION=12946]Delta[/MENTION] came through. I didn't get my preferred routing but they were able to give me a second-choice routing (BWI-DTW-JFK-YUL) which I found three seats' availability on and they confirmed. Made a point of thanking [MENTION=12946]Delta[/MENTION] for the help (generically, mind you) publically.

In short? For the first time in my life I have a use for Twitter.

Edit: [MENTION=206647]javabytes[/MENTION] has what the website states. A reasonable part of why I am so happy to pay for F is because of the stated policy (even at $75/SDC instead of $50). I have, quite literally, only booked a fare containing a Y segment once and that was only because I was stuck with a DSM-MSP-DCA routing (IIRC) due to timing constraints around a funeral.

If Delta wants to change their policy so that there are intra-premium-cabin restrictions then that's one thing, but as things stand the website states that F/P/A/G and J/C/D/I/Z are all interchangable:
"If you have a premium cabin fare, -- including Delta One?, First and Business Class -- you may make a same-day confirmed change as long as a seat is available in the premium cabin."

That's a direct (if slightly flawed due to copy/paste issues) quote. There's no mention of routing restrictions (other than the general rules such as above) nor of fare class restrictions (merely cabin class restrictions, and the interchangability of the "Business" and "Domestic" classes makes sense since there are a lot of flights which have J-related fare classification on domestic routes), and the website makes no attempt to advise of any other restrictions which might affect the above for an F fare.

since they DID give you a routing change, what was the reason given for why your preferred routing could not be given?

Lack of availability on my initially preferred routing (which is still showing a free seat as of right now).

I don't understand the OP's reason for even making these changes to the awkward new routings he is looking for (for three different travellers in the current example?).

I could give several answers which are all technically true, but the rub is that I'm trying to pile up DL segments for VS status prior to that rules change happening. Thus my preferences, in order, are:
(1) A workable time of travel that lets me have dinner in Montreal, then
(2) More segments (since VS status is more-or-less based on segment count), then
(3) Segments long enough to get a meal, then
(4) More mileage (since VS still awards mileage based on distance traveled instead of money spent).

Cost is relevant as well, but it applies in the context of 1-4 rather than being a solely independent variable (e.g. I'll happily pay an extra $50 for an extra segment). 3/4 are also pretty much a tie (and often go together), but I'll usually trade a few hundred miles for not having to scramble for food on a layover.

Edit: This would still be relevant if I were chasing DL status as well, but it's somewhat moreso on VS.

Edit 2: There's only one traveler (me), hence the frustration. Mind you, I have friends who would likely enjoy joining me on such a wacky routing and others who would tolerate my craziness. The relevance of there being three seats is more that "There is more than one seat available so there really shouldn't be a reason it's tied up".

My impression across various SDC experiences is that some SDCs, although permitted by the rules, are not automatically recognized as valid by the system. In such cases the SDC requires some sort of manual override/processing, which it seems that not all agents or supervisors know how to/feel motivated to handle (and they may not be aware of the full extent of the rules).

I would also guess PM/DM line agents are more likely to do the right thing the first time out.

It can be frustrating, for sure, especially if HUCA means a long wait on hold.

So this is a waste of the airline's time.

Won't this sort of thing help to kill off the SDC program and thereby its use by folks who are trying to actually get from one place to another?

It's only a waste of the airline's time because they have so poorly trained their staff not to be able to handle a simple within-the-rules SDC request, and any call to do so (regardless of the traveler's motivation) turns into a protracted debate with agents, supervisors, and/or the Twitter folks over what the rules actually are. And because the website fails to adhere to the rules either, often failing to find available options, or trying to charge for what should be free, thus eliminating a self-service option that would cost the airline zero time.

Wrong.

You can SDC a FC ticket directly into FC if FC seats are being sold on the new flight. There's no fare class availability restriction for FC tickets, which is what the OP has (class A). [The same is not true for coach tickets.]

Also, you can change the routing on a SDC (but not SDS) assuming that the new routing is legal for your fare and that you are not changing from a connection to a nonstop. If you have a broken fare, you must go through every airport where there is a fare break.

These are the published rules. DMs are allowed co-terminal changes.

See javabytes's reply; but I'm genuinely curious what percentage of CS interactions you think concern SDCs (successful or otherwise).

[MENTION=9799]Justin026[/MENTION]:
So let's see...DL has gotten me to pay about $650 for a round-trip ticket which I could likely have booked in a discounted Y bucket for about $250-300. Even offsetting that with some benefit for comping a Diamond into First, I believe that allowing this is a rational choice on the airline's part, particularly as the airline has been trying to induce paid First fares to improve flight yields. Moreover they arguably induced the trip, at least in part, by my ability to do this (had this not been on the table there's a good chance I would have been on an early morning Amtrak train instead). Finally, given that all of this is happening inside of 24 hours from the flight going out the door, I believe that DL at some point determined that they really don't care which seats their paid First pax filled since I'm only possibly blocking out a de facto walk-up ticket and DL appears to have determined that there aren't many of those to be sold anymore (particularly in the front of the plane).

The only "wasted time" is due to the ineptitude of their IT department to set up their website to recognize their stated SDC rules for premium cabin passengers who are either relatively high status or willing to pay for their changes. Considering the rather colorful history of DL and their IT department, I am inclined to think this whole exercise is a result of them flubbing an "upgrade" in the past. If it weren't for this bumbling, then I wouldn't be stuck going through an exercise out of a Terry Gilliam movie to do a within-the-printed-rules change.

If they want to restrict routing and so forth on SDCs I don't fundamentally have a problem with it, but they need to do so by actually writing passenger-facing rules that openly implement such a restriction rather than relying on a bunch of IT kludges to deter it. If they change their policies then I will amend my behavior accordingly. But if they are going to try to informally implement a bunch of rules in a passive-aggressive manner then I have a very real problem with that. The fact that at one early stage I was told that there were no SDC-qualified seats available really points to an agent/computer problem (especially when I could find quite a few scattered over dozens of website-listed routings).

And if you're surprised that someone on here is trying to work airline routing rules and so on to their maximum benefit then I have to wonder how long you've been on FT. All I can say is that this is nothing.

Edit: And of course, someone beat me to this with a more succinct statement.

Exhibit A of what I use SDC for:

Maybe the agents are pushing back because the requested routings are absurd? They hear an absurd request and it has them looking for the reason why the rules don't allow it.

Adding out-of-direction segments to replace confirmed nonstop service or straightforward connections in order to earn credit on another airline and/or eat extra meals in flight? And wondering about hiring a lawyer if the airline says, uh.... "no" ?

... and when they don't find a reason disallowing it, what's the excuse then?

I do agree with you you that threatening legal action is over the top.

Still curious re: wasting the airline's time, what percentage of calls you think involve a SDC.