@darkmatter: well then just try to wear them for a while. usually the waistband stretches back to raw measurements on unsanforized denim. since you found them at a thrift store, I guess you don't care about "losing value" on those jeans by wearing them a little bit.
lined back pockets are mostly done on special editions or collabs.
s5000bk is a regular cut and so no lined back pockets
s5000bkb was first introduced this year but also no lined back pockets (AFAIK)
if the Black shadow or BKII don't have lined back pockets, then Gordon from BiG didn't ask for it.