This is what we refer to as "bricking". In baseball, it has been seen from the 1993 Upper Deck set through to at least the 2002 Topps set. Many methods have been tried to separate the cards without damaging them, everything from freezing them to steaming them. About the most effective way is to take the brick and bend it from both end as well as giving it a slight twist. You will hear them come apart. But if you look closely at the cards, (some don't need really close inspection) you will see some of the ink having flaked off and stuck on the other card. At times,the paper will also actually tear from one card to the other. But as Billy has said, the damage has been done.
Store these sets very loosely in a box or with penny sleeves froeach and every one, or in a binder in 9-pocket pages.
Bruno
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Check my Profile page to see my 2023 Goals and my Lists of sets near completion (5 cards or less) or sets getting close (less than 100 cards missing and 75% complete).
https://www.tcdb.com/Forum.cfm/Page/B/ID/0/?MODE=VIEW&ThreadID=25745&C=0