Several of us have seen what appears to be an internal Delta graphic that instructs agents how GUCs and RUCs apply in different cabin/aircraft scenarios and what specific inventory buckets are needed to confirm GUC/RUC usage. This data has been updated in the WIKI both here and in the Regional Upgrades thread. It also outlines how the new delta.com Upgrade Availability flags work (now there are 2 flags "Global Upgrade Certificate Available" and "Upgrade Certificate Available") and examples of each scenario.

New Fare Table for GUC/RUC Effective 2/1/2022

*****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)

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)