Just used RUCs for the first time this past weekend...here's my experience.

Booked a MR flight back in Sept: CHA-LAX, stopover night, LAX-MSP-ANC with return two days later: ANC (redeye)-MSP-LAX-ATL-CHA to get extra mile for Diamond.
Turns out that my one full day in ANC is my oldest daughter's 21st birthday - she lives in SAN so I booked her a flight to match our LAX-MSP-ANC and return.
Then, I asked my youngest daughter (age 12) if she would like to tag along with us, so I then booked her flight to match mine.

Ended up getting Diamond last month so this became a fun birthday present! But I used my Plat gift before getting Diam to get 4 RUCs which I applied to this weekend and planned to give both my daughters the FC seats.

True to the fine print, I couldn't use the RUCs for my daughters, it had to be me and a travel companion. Luckily, when I called (after purchasing tix) the Delta agent linked my 12yr old and my records so she wouldn't be an unaccompanied minor and the RUCs would apply to her.

After that setup, it looked like we would be waitlisted for LAX-MSP, MSP-ANC and MSP-LAX but cleared for the redeye ANC-MSP.

Done, right? ...LOL!

Anxious to see if we cleared anytime before the flight, I kept checking the Delta app for my account and my 12 year olds.
No updates up until check-in (24hrs out), but I couldn't check in because I'm flagged with a minor. [sigh] Get to airport, day of, check in and grab first leg to ATL where we had decent layover. In SC, I notice that my 12yr daughter has multiple bookings - some in coach, some as waitlisted FC...as did I (but only one)

Talked with counter agent in SC to look at situation. He clears my coach double booking, but say I need to call reservations to look at her record (of course he is near the end of his shift I hear him saying to others behind counter)
Call DM desk, what I think she said (in broken english) is that since we're checked in, it's under airport control - need to see an agent.
Go back to SC counter and talk to different agent (because original is gone now). She looks at record and says she can't do anything about that, so she calls reservations.

<<<Now I'm starting to feel like those ever bouncing back-n-forth set of pixels on the screen of a Pong game>>>

She sits for 15+ minutes listening to the res desk agent typing away. Meanwhile, our flight has started boarding so she agreed to hold on hold to get it resolved and we'll check back with it in LAX.

Upon getting signal in LA, I check our accounts to find what has been fixed: her (and I) are upgraded for the LAX-MSP and MSP-ANC flights the next morning and waitlisted for MSP-LAX, but now she literally has no ANC-MSP flight listed..?!?

Call DM desk again to find out that what actually happened is that she has cleared the ANC-MSP upgrade and she put it back in the record (or something so that I saw it on the app)

On the outbound flights, I decide to check in again, as I cleared both segments to and out of MSP, but my 12yr old has not cleared the MSP-LAX leg. I had been told once that if I clear and keep my seat, but she doesn't clear, that I would be hit with an unaccompanied minor fee. But I ask that I plan on giving my seat to my 21yr old daughter, and take her seat in back. So we juggle seats in coach so that my 12 year old and 21 year old are seated next to each other just in case she doesn't clear - and the agent puts my 21 year old as a travel companion with the 12 year old so that I can keep my upgrade and swap with my 21yr old.

Sound complicated yet...it gets better...

After checking in at ANC, getting boarding passes as I check luggage...I notice my 12yr old has not been checked in (on the app). She doesn't show up on the upgrade list for MSP-LAX, yet she shows up on the LAX-ATL upgrade list (down near the bottom as my DM companion) The counter agent says she is on there, and should clear (even with only two seats remaining and 75 people on the list (with my 21yr old listed as 72nd as a Silver)

Bothered by the lack of "Checked in" I call the DM desk again from the Alaska lounge. I'm asking why my 12yr old doesn't show up on the upgrade list for MSP-ANC. She says we'll have to check a Delta agent at the airport (insert another quarter for another round of Pong!!!) But after asking her several times why she shows on the waitlist for LAX-ATL and that she has cleared the previous three legs, what is the problem, she puts my on hold for nearly 10 minutes.

After speaking with a super, she was told that because:
- my daughter was a minor
- she was on a separate record
with those two factors, she was on a "special" list at the MSP gate that only that agent could see and clear, once we get to the airport in MSP.

I check again with the gate agent in ANC who noticed on the computer that the guy who checked us in at the counter was still working on the my daughters record to get it 'fixed' - this is at least an hour after we checked in downstairs...???
So we leave ANC without any resolution and get to MSP where luckily our connection is the next gate over. End up waiting for agent (red coat) to show up, she looks at the record and sees what looks like the length of this post in there - except written by 7 previous employees that I've spoke with so far about this one trip. Then she says she has no idea how RUCs work and called the main Delta desk who looked into it and eventually said she was on the list but not showing up on the app or the overhead screens at the gate.

Oh well...

But then, about 10 minutes before the flight started boarding, she showed up in app and on screens: #1 of 85. Two minutes before boarding her name disappears...wonder what that means...should be upgrade, but app still shows 34A.

As we scanned passes, she did get the upgrade and my daughters continued their snooze fest until we got to LA.

Along the way, I found out that the RUCs were not applied to the ATL-LAX and LAX-ATL legs because those two segments were in a different fare class - X instead of V - which probably would require additional RUCs.

After the fact - it was good to get to use the RUCs on the legs and to find out allot about the "system" limitations and procedures: i.e.: call to confirm several times until programmers figure out how to apply special circumstances that have not been accounted for.