Had noticed this too because I collect certain managers and found they were linked even though not pictured. If we linked every card to anyone mentioned on the back, it would really invalidate player collection lists.
Not sure what reasoning the individual(s) had in doing this but hope it was ignorance of the rules (not an excuse) and not because of personal collecting practices.
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