Compass mins are actually 2500 total and 1000 MULTI time (or 2000 TT w/ 1500 multi) per the contract. I can't find anywhere that compass specifically requires solely 121 sic time to satiate the FAR 121 upgrade mins. Except for in flica when the system asks you input your "121 sic time" each vacancy bid when trying for captain. I doubt that's the case, rather I think it's crew planning's shorthand method of asking if you're legit before trying to go for upgrade.

The reg (121.436 (a) 3) says the 1000 hrs can be any combination of following:

121 sic time
91k (net jets etc...) multi turbine pic
135 turbojet pic, or 10+ pax seat pic, or commuter multi pic