Having done similar entries in baseball where I had cards that I wanted listed in my collection and duplicates that I wanted to list for sale / trade, I found that the quickest way was to enter as Tigerfan22 described above clicking on the boxes to enter the cards that I had for sale / trade into my collection and then moving them all to For Sale / Trade. If I had most of the set for my own collection, I would then add all cards in the set to my collection and then remove those I did not have. If I was looking to complete the set through trades, I would then add the missing cards to my Wantlist.
I understand it can be a long process to add more than one of any one card to your collection. I wish that whether I had a card or not, I would always have a box to simply check in order to add another to my collection.
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