Will the SDC option within the website's online check-in process display co-terminals? AFAIK this is an unpublished DM benefit, but I'm guessing my only option to SDC to a co-terminal flight when the original flight was upgraded with a RUC is calling (which has a lower success rate)?

When it's working, I think the answer is yes ... you may need to manually change the search parameters (e.g. from JFK to NYC). Back before app SDC became broken recently, it generally handled the DM coterminal benefit seamlessly and presented coterminal options automatically, other than that it would not give options to change from a nonstop to a connecting itinerary.

I too would be very interested in knowing the KM terminology that allows RUC SDChanges. On the occasion I try to make this change and retain a seat in first class (after RUC is re ticketed), I get lots of pushback and as noted above, it takes a LOT of TIME.

I can't quote KM here, but the language quoted should work to enable them to find it.

I have a flight in a few months from BOS-LAX-SFO. I was able to use a RUC at booking to confirm into D1 on the BOS-LAX segment (now showing as OX), while the LAX-SFO segment is in C+ (SU). I may want to SDC to BOS-JFK-SFO. Is this possible, or am I limited to LAX connections? If so, will I be able to stay in D1 on the JFK-SFO segment?

You most likely won't be able to do this unless the entire itinerary clears and is re-ticketed first. Then, be prepared for a fight to be able to make it happen. While technically a change of connection should still allow a SDC and keeping the RUC applied with any seat in F, once you add in the change of connection city and the fact that D1 is involved, expect a lot of push back from the agent before they finally push it to re-ticket.

Though I'm not sure the policy, doing a SDC with only one leg cleared results in them saying that you are not entitled to stay in F (unless RUC space is available at that time).

Thanks for the quick reply. That's kinda what I expected, but welcome the confirmation that it will probably be problematic.

Is that LAX-SFO segment available for upgrade now? You'll need Z inventory to upgrade. You'd need to call and they can apply the same RUC you used for the BOS-LAX segment to the other one assuming its available, or even waitlist you for the upgrade on it in case Z becomes available. I would not trust the online system to actually have you waitlisted since it cleared the other one.

If you're not in first on both segments I wouldn't expect an SDC to work for what you're wanting to do.

I've cleared JFK-LAX about 3x in the last 2 months and each time it's taken 2-3 calls to find an agent to help complete a SDC. Most of the time they have no clue what they are doing. One guy made me pay $75 to change (for myself, not companion) and upgraded me again, even though no UG space was avail. Why is this so complicated?

Only I inventory available on the LAX-SFO segment at the moment, but good point about calling to waitlist. I don't see any indication that the online system did so.

Yeah unfortunately with the new horrible UI for mytrips and viewing itineraries, there is zero indication if you are waitlisted for an upgrade. The old UI used to have something like 'upgrade requested' below your seat and class indication.
I also experimented with this and had a domestic flight with RUC supposedly waitlisted using the online system and nothing happened when Z opened up for several days. I ended up calling and they processed the upgrade so I have no confidence that the online system actually does do a waitlist if you select a cert while booking.

Tried SDC'ing a flight after checking in. On the app, it says PNR is not eligible for SDC. On the website, standby's only. Decided to call.

Agent 1: We would have to undo the RUCs(outbound and the inbound) and move you to main cabin(new flight), then apply RUC for upgrade. Me: Um, no thanks. Please, don't change anything!
Agent 2: We can try after un-checking you. Me: okay, go ahead and try. Agent: same story as agent 1. Me: okay, I'll just fly my original flight. Agent: Would you like me to check you back in? Me: It's okay, I can do it.
Can't check in with app or website. Called to fix check in, gave up on the SDC.
Agent 3: I see what's wrong. I need a few minutes. Me: okay. Agent: You're all set. You can check in. Me: Thank you.

Just for kicks, I check the website for 'confirm'. Lo and behold, I see some options. I didn't get the flight I wanted but the one leaving after. Now, I don't have to trek through NYC in the wee hours of the morning.

Data point: same as previous poster, my cleared-RUC itinerary says "PNR not eligible for SDC" in the app.

Using change flight on the My Trips page on the website, I get a similar error. However, by going through the check-in process on the website (even though I'm already checked in), the change flight option that appears on the page reconfirming your flight details offers me the expected options to change to any other flight that day with open premium seats. As before, that interface doesn't super clearly indicate that it's offering D1 on the other flights, but it does mention "business" at the top of the page. I don't actually need to change though so I didn't try it to see.

Separate RUC issue, I had originally waitlisted the upgrade on this flight using the checkbox while checking out on Delta.com, but I was nervous whether that worked so I called a couple days ago and had an agent manually waitlist it. (It's unclear if I was really waitlisted or not; it appears that if the website waitlist function does anything, it does so in a way that's not visible to the agents.) I got upgraded a few hours later, alongside a few others to judge by seat map changes, but I guess hard to say if the call had anything to do with it.

https://cimg4.ibsrv.net/gimg/www.fly...74f056a2c8.jpg
Click on "Change Flight" at this point in the web check-in process

https://cimg6.ibsrv.net/gimg/www.fly...08a4e963ba.jpg
No 100% clear indication that the alternative flights are still in business, but it does say Business at the top of the page

Agents are insisting upgrade class (OL) has to be available on the new flight to SDC... I even asked to check under knowledge management but the response was "I have been doing this for a long time and this is a voluntary change"... Time to waste a whole day with HUCA


EDIT: HUCA #2, reached a great agent who knew the policy! Apparently the prior agent ("I have been doing this for a long time") had put a note on my reservation saying OL class must be available for a same day change. This agent knew that that is "simply incorrect" and removed that BS.

Have you tried the Delta.com OLCI process as noted in my previous post? Finding an agent who will do this seems increasingly rare these days.