Well, in a way, it wasn't "necessary" for Criterion to add the sequel, given that WAC released a triple-feature set of all three of the 70s Shaft movies. In another way, it's almost sad that they aren't including the third film, but since this release is something of a celebration of Parks, it...
I'm surprised that no one had yet commented on this special feature:
Shaft’s Big Score!, the 1972 follow-up to Shaft by director Gordon Parks
Yes, it's just on regular blu-ray, but...