That standard is addressed here as the 4 max WB and as outlined within MTP and emergency release policy.
A previous facility I worked at used WB for MTP until they ran out or were able to complete the Type and screen +ABOconf. Then XM PRBCs/FFP/PLT/CRYO rounds. The time frame there was per MTP, with unknown blood type. Tricky thing at my current facility is that WB is first two rounds of MTP regardless of current testing or blood type, so theoretically they could qualify for WB again with a new MTP activation, or under a new admission per se.
Maybe I'm thinking about this too hard, but the SOP I'm working with seems a little thin and hasty. Why give uncrossed Opos WB to a patient you know is Apos (current T&S) just because they're initiating MTP? Only thing I can figure is that it's quicker to issue 2-4 units of WB versus a 4/4/1/ or a 6/6/1 MTP round.