Let me clarify this better. Your 1990-91 UD NHL packs will only include card #'s 1-400 in the 1st Series but could be 2 different holograms on the backs of the cards. In the 2nd Series packs, there will be cards from the full 550-card set and they will still have hologram differences on the backs of the cards. Yes, a single box of Series 2 cards does include all 550 cards in the set, but you probably won't pull a complete set from one box. That was the detailed answer.
For the simple answer: YES! Buying a High Series box will give you cards from both Series 1 (Low Series) and Series 2 (or High Series). You won't complete a set from a single box though.
NO PWE's EVER!!! PLZ PM me 1st before sending a trade or buy offer.
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Largest total PC card collections by Team, then Athlete (as of 3/31/23):
STL Cardinals (MLB) - 8700+; Carolina Panthers - 2800+; GB Packers - 1700+ cards
Mark Martin (NASCAR) - 2034 cards; Jimmie Johnson (NASCAR) - 1776+ cards; Jeff Gordon (NASCAR) - 1563; Ricky Rudd (NASCAR) - 828; Ozzie Smith (MLB) - 692+