Originally Posted by
audidudi
This is all that is on DL.com referring to the class of upgrade fares that are eligible:
Valid on Delta-marketed, Virgin Atlantic-operated flights for use globally on published Economy Cabin fares booked in W, Y, B, M, S, H, Q, K, L, U, T, X or V class to Upper Class.
That doesn't help any for what bucket it books into on VS. We know the Delta buckets, but there is no mention of the inventory needed to upgrade into.