[rant mode]
...what - nobody knows...??? Well that must be because THERE IS NO STANDARD - it must just be whatever mood they are in that batch...

I pretty much buy all my clothes at either Rural King (jeans, underwear, socks) or Goodwill (shirts, sweaters), other than I spend the money saved on great shoes, since if I don't my feet hurt like crazy.
But no matter where I get the jeans (I occasionally stray from RK) and no matter whether I get a 'name' brand like Carhart or whatever, it seems like when I do my weekly 'move-in' to the new jeans-for-the-workweek, the belt-loops are always in different and unpredictable places.
That makes it a real pain-in-the-sacrum (literally, sometimes) and annoyance when it comes to positioning some of the EDC stuff, due to loops being too close together for the magazine/multitool carrier I like, and/or in the wrong position for comfortable use of my IWB holster.
Maybe next time I need jeans I'll see if RK has about 20 pair in my size, then take one to the dressing room and see if it accomodates my 'stuff' - and if it does just buy 20 pair or so at once (that is, IF they have the loops in the same place). I swap 'work' (office) jeans weekly, and after about 6-8 cycles a pair downgrades to 'grocery store' status, then another 6-8 and they become 'family picnic' ones, then 'yardwork' ones, and eventually 'changing the oil' ones, and I feed 3-4 new pair into the rotation every 3-4 months, so I guess I 'consume' a pair per month maybe - so 20 pairs might last a couple years.
[/rant mode]