I don't know how it happens.
I like to think my level of organization is very high. But time after time, I get cards in the mail and check 'em off my want list site, go to put 'em away, and the same card is sitting in the box or binder already.
I make thorough lists from reliable sources. I try vigilantly to check them off before putting them away. And it should be easier for me since my computer is in one room, and my collection is in the other. So I open the packages and set them by the computer, check 'em off and then have to actually walk them over to the adjacent room.
But still, it happens. Or, it's the other way. I get down to the last card in a list, get it, and then go through the set just to make sure, and find several numbers missing. WTF? I often hear other collectors call that a Gremlin Attack.
How do I cross off numbers that I don't actually get? Or did I cross them off and then put them in the wrong pile and trade them away somehow? Who knows....
This just happened this past week with three sets that I thought I had finished. Had two of them on my Priorities page on my website (new link at left or here). That's where I put the most important cards I'm looking for at the moment. But it turns out they weren't the sole survivors.
Still need these: 23 Clemens 133 Orie 268 DeJean RC 351 MVaughn Hit List 367 Jeter Hit List 378 Mussina UTs
Jeter. Always Jeter....
5 Walker Star Power 21 Scharrer Draft Pick 38 Belcher
Really? Messed it up TWICE!
And these two were what I had listed as the last two 1993 Donruss. Somehow, even though you might think it's easier to do in a large set like this, I still didn't have these in the box:
141 Nagy 466 Cox 559 Ripken 631 Fletcher 729 Edens
Could'a swore I had Cal....
And even this one. Beckett had a partner for a good while, until I got that one. He then stayed on the list by himself until he finally showed up in a trade. Went to put him away, and "Gah!" he was already there.
Watch out for gremlins this week. They're on a roll!
Let me know in the comments if you have any way to keep them in check....