I didn't think it is the priest's ordination directly that is the issue, but the consecration of the Bishop doing the ordination that is the problem. If the Bishop was consecrated prior to 1968 ( even Novus Ordo 1968) it was a valid consecration and not a Vll "installation" as the consecration for bishop was changed to the point of nullity at that time.
I know this is not news here at CI, but point being there may be (rare) valid priests left in the NO and FSSP that were consecrated by a (old) valid Bishop. Doesn't validate the NO Mass however, but I wonder about the FSSP.
I knew an FSSP priest that was ordained by JPll- a modernist Pope, but a Bishop prior to 1968. I suspect he is validly ordained. Few and far between, however, and getting thinner by the year.