To my knowledge, Pearl's American market never offered these. I either own or have access to all of Pearl's American market catalogs during the Wood-fiberglass and fiberglass eras. A denim wrap is just not there. Now, that doesn't mean they weren't offered in other markets...
Anyway, for what it's worth, I have seen a denim wrap on PWG drums before. An eBay listing a couple of years back. Maybe these are the same ones; I really have no idea. My best guess, however, is someone has rewrapped them themselves... copying the idea probably from the Slingerland kit that was done back in the mid-to-late 70s.
All that being said, as to value there is probably no real "collector" value here at all (which is the case with PWG drums anyway -- I know, I've moved a few of these sets and they just aren't in high demand). If you like them and are going to use them, pay what you're willing to pay... I still own a set I bought new in 1978 and they are good drums!