Whoa... Mind blown. I just bought some music... based off j_menz (and others) comments on here. But if that's me from the future, then I just bought those edition j_menz was talking about in a post from a while ago.

It's a circle in time.
The answer of course is that I always bought these books. j_menz just happened to contribute comments. Otherwise he wouldn't have had the books in the first place.
Unless... I acquire the books some other way in my future and that's what j_menz has. However, now I've purchased the books. I didn't do that in the original time line, so j_menz's comments must have influenced me to purchase. But he'll have the copies I purchased now. That could screw up the time line for when I/he comes across the original copies he had. Which means in this case, I/he end up with two copies of the edition.
*Bob considers scarring himself and then checking if j_menz has posted in the past about scars...*

Now that I've thought of it though *and* posted this idea... I/he would be smart enough *not* to post anything about scars. So that might prove it, whether I scarred myself or not now.