Thick Modern Cards ?
 

I don't deal with the 21st Century cards very often, but at times I get a collection that includes these cards. Some of the cards are thick, but appear to be the same in all other aspects. Are the thick cards short-printed, do they carry any additional value ? When ( what year) did these "thick" cards start and are they still being issued in packs ? Thanks

I think they started in the late 90s when they were adding relic/memorabilia cards into packs, so that you couldn't easily pack search and determine there was a "hit" in the pack. So some are used as decoys instead of just having a white cardboard spacer in every few packs.
I first recall them in like Score Board packs (or something else unlicensed) that did draft basketball sets with Kobe Bryant on one side, and a different player on back.

Some are hits, some are not. They were still being issued in packs (especially Panini) to deter pack searching, as recent as a couple years ago. COMC even calls those extra wide base cards "Decoy Thick Stock" parallels. Even newer cards are numbered even without a relic may be extra wide. I bought a box set of Topps 2019 Art of the Teenage Mutant Ninja Turtles and every card in the set, base or inserts, was thick stock (except the sketch card).

Some of the super high end products like Exquisite, the Cup, and National Treasures use 130 point stock for the base cards! They're so thick you can stand them up on their edge.

Exquisite released in 2003.

I remember in 2010 buying a box of Ringside (boxing) and being so disappointed that it was printed on super-thick stock. What a PITA. Doesn't fit the abundant top-loaders and sleeves I had.