We’re talking about Fox’s Blu-rays of 1-6 vs Disney’s digital copies. Fox is going to release the same discs every second until 2020 is over.
As for being the same stock, I doubt they have warehouses full of printed discs that every few years they put into a different case. And it’s not like they recall a store’s stock, rip open all the sets, put them in different cases, then send them back out. I imagine this is Fox having finalized disc images that they don’t have the rights to modify any more, so they just reprint them over and over.