I got the screen worn outfit I was asking about in an earlier post, and the sweatshirt (which I compared to the scene in the movie) even has small flaws which are identical to the shirt shown on screen, but the seams on the back of the shirt's neck seem to be in a different place than on screen.
Am I making any sense?

If you can match up some imperfections exactly then I suppose the seams you think are in a different place are due to how it is being worn. It just appears to be different. If you can send me some pictures of your shirt and the scenes its used in I can take a look. Email them to mrmovieprop@movieprop.com
Also it is possible more than one shirt was used in the scene you saw. One you can match up the imperfections that is yours, the other that you see seams at this is not yours. If the scene was shot over a few days or someone spilled something on it the shirt would get changed out for another. Is the shirt labeled in the collar or via a costumers tag?

Actually, now that I look at it again, the seam I thought was in the middle of the collar is actually on the edge of it. (the side I thought was half the collar seems to be just part of the shirt) I do not have a costumers tag but a couple of imperfections do look identical to what is on the screen, and as I mentioned before, this outfit came from New Line Cinema (with a COA.)

Is the shirt marked on the inside? Not all wardrobe is marked but typically it is. If it came from New Line Cinema they probably had all of her outfits in a rack or container together so they would know if its not marked and the costumers tags were removed at some point.
At least you got a movie item so you could watch the whole movie to look for the item. Try getting a Buffy shirt item from unknown season and watch several seasons of that to look for it. Thats why I tend to avoid TV wardrobe items if I don't know the season or episode its from.

Nope, no tags or studio markings, just identical flaws in the same places as on the screen.

If from them that way its ok. If from someone you are not familiar with its not. Its just something to look for.

By "them" do you mean from New Line Cinema?

By them I mean New Line Cinema as compared to an unknown source of low reputation for example.