For discussion of same-day change on an itinerary with an RUC applied, see: SDC while using Regional Upgrade Certificates (RUC) Definitive Thread

FEB 1, 2022 New GUC/RUC Inventory Rules

*****GUC*****

Flight has First Class
MC/C+ = Purchased
First = Last Seat J (Old Policy = OY)

Flight has DPS only
MC/C+ = Purchased
DPS = Last Seat (GUC=P / RUC=G) (Old Policy = RY)

Flight has D1 with no DPS
MC/C+ = Purchased
D1 = Z (Old Policy = OY)

Flight has D1 with DPS
MC/C+ = Purchased
DPS = Last Seat (GUC=P / RUC=G) (Old Policy = RY)
D1 = OY @ T-24h15m

Flight has D1 with DPS
DPS = Purchased
D1 = Z (Old Policy = OY)

Note: If GUC applied to domestic flight, it has better inventory than RUC (better chance for D1 transcon or to Hawaii)

*****RUC*****

Flight has First Class
MC/C+ = Purchased
First = Z (Old Policy = OY)

Flight has D1 with no DPS
MC/C+ = Purchased
D1 = OY (no change in old policy = OY)

Delta is using public inventory buckets J Z P G (and non-public bucket OY in some cases) to determine GUC/RUC availability. However once they have confirmed you the system converts the segment in your reservation to a different bucket. Here is the class mapping:
GUC Usage
MC or C+ purchased / Upgrade to DPS / P class needed / Books into RV (Clears at T-24.15 into D1 as OX if OY available)
MC or C+ purchased / Upgrade to D1 (no DPS) / Z class needed / Books into OK
DPS purchased / Upgrade to D1 / Z class needed / Books into OK
MC or C+ purchased / Upgrade to FC (no D1/DPS) / J class needed / Books into OV

RUC Usage
MC or C+ purchased / Upgrade to DPS / G class needed / Books into RX (Clears at T-24.15 into D1 as OX if OY available) ****THIS AIRCRAFT CONFIG MAKES NO SENSE DPS IS NOT SOLD ON RUC ROUTES, MAYBE THIS IS FOR FUTURE PLANS?****
MC or C+ purchased / Upgrade to D1 (no DPS) / OY class needed / Books into OX
DPS purchased / Upgrade to D1 / OY class needed / Books into OX ****THIS AIRCRAFT CONFIG MAKES NO SENSE DPS IS NOT SOLD ON RUC ROUTES, MAYBE THIS IS FOR FUTURE PLANS?****
MC or C+ purchased / Upgrade to FC (no D1/DPS) / Z class needed / Books into OL

New Delta.com Upgrade Availability Indicators that appeared 2/1/22 and what they mean

Dom D1 Tag meaning:
Global Upgrade Certificate Available = GUC in Z (OY = 0 for RUC)
Upgrade Certificate Available = GUC in Z /or/ RUC in OY both available

Dom F Tag meaning:
Global Upgrade Certificate Available = GUC in Last Seat J (Z = 0 for RUC)
Upgrade Certificate Available = GUC in last seat J /or/ RUC in Z both available

Example D1 Flights from JFK - LAX (flight numbers are fictitious)

DL 01
Dom D1 flight
Actual Availability: J5 C4 D4 Z3
Hidden Availability: OY2
Website indicator: Upgrade Certificate Available
Actual decode: (2 RUC (OY) open, 3 GUC (Z) open)

DL 02
Dom D1 flight
Actual Availability: J5 C4 D4 Z3
Hidden Availability: OY0
Website indicator: Global Upgrade Certificate Available
Actual decode: (0 RUC (OY) open, 3 GUC (Z) open)

DL 03
Dom D1 flight
Actual Availability: J3 C2 D2 Z0
Hidden Availability: OY0
Website indicator: No flag - neither is available GUC (Z0) and RUC (OY0)

DL 04
Dom First flight
Actual Availability: J3 C2 D2 Z1
Hidden Availability: n/a
Website indicator: Upgrade Certificate Available
Actual decode: (1 RUC (Z) open, 3 GUC (J) open)

DL 05
Dom First flight
Actual Availability: J3 C2 D2 Z0
Hidden Availability: n/a
Website indicator: Global Upgrade Certificate Available
Actual decode: (0 RUC (Z) open, 3 GUC (J) open)

DL 06
Dom First flight
Actual Availability: J0 C0 D0 Z0
Hidden Availability: n/a
Website indicator: No flag - neither is available
Actual decode: (0 RUC (Z) open, 0 GUC (J) open)

I’m not able to check-in online for a flight where RUC/GUC was applied.
The problem is most likely that your upgrade cleared but your ticket has not been re-issued. Call to request a manual re-issue of your ticket.

__________________________________________________ __
PRE FEB 1, 2022 WIKI
More information and discussion about using same-day change after applying regional upgrades can be found in this thread: https://www.flyertalk.com/forum/delt...ve-thread.html

• The clock begins ticking on RUC expiration when you make your choice benefit selection, so it's possible to time your selection when there is a specific need to use them.
• You can select your 2017 choice benefit as soon as DL recognizes your Plat status. Certificates expire 12 months from date of issue. 2019 choice benefits (earned based on how much one flew in 2018) must be selected by Jan 31, 2020.
• If you select certificates as your choice benefit late in your Medallion tenure, it will still be valid after your status expires -- so for example if you earn Platinum Medallion in 2018, which is valid through Jan 31, 2020, but then only earn Silver Medallion in 2019, which becomes effective Feb 1, 2020 when your Platinum Medallion status expires, RUCs selected in January 2020 would be valid through January 2021 and could be used once you were only a Silver Medallion member, giving you a much higher upgrade list position on those flights where you attempt to use them.
• If you request to use a RUC on a flight and do not receive the upgrade, it is returned to your account for future use, but check your account to make sure.
• RUC may be redeemed for the named Medallion member and up to one travel companion traveling on the same flight (the companion officially no longer needs to be in the same reservation, though that rule was not actually enforced even when it was the official rule). The named member and the companion will each require a separate certificate.

While the RUC process is almost entirely opaque, there are a couple of "hints" of a correctly applied waitlist.

1a) When viewing a waitlisted segment on the DL.com web site (not the app), there may be two seat maps for the same flight. The first seat map shows the coach seat you are currently in, and the second seat map for the same flight says "you may not select seats for this flight" or something like that. This second seat map corresponds to a part of the waitlist process, and indicates that at least one step of the multi-step process to add an RUC waitlist was actually done. Unfortunately, this does NOT indicate that the other manual steps of the RUC waitlist process were successfully completed by the agent (i.e. even if you see the second seat map, there still could be something wrong. There is simply no way for the customer to tell.)

1b) The status for a waitlisted segment should say something like "Upgrade Waitlisted"

2) Assuming the waitlist does not clear prior to check-in, the second hint is the upgrade waitlist. If the RUC waitlist request was coded correctly, you should show up at or very near the top of the upgrade waitlist that you can see on DL.com or the app. If you find yourself at your "usual" spot on the upgrade waitlist, this is a clue that the RUC waitlist request was not coded correctly.

3) The RUC is a form of "payment". Until the RUC clears, it remains "unused" so a waitlisted RUC will still show in your wallet as "open".

You may also wish to peruse the wiki for the GUC success thread as some of the considerations/logistics are similar between RUCs and GUCs.