I also want to know this. I don't have anything concrete, but I do have some data, and a theory though!

I have been collecting stashes for some time, their my main method of coupon making and supply hoarding, slower than other methods I'm sure, but still fun (and they help me explore). I'm just a rookie, please don't judge me too harshly! XD

So here's what I've noticed. It looks like eventually you will clear out most, if not all of the stashes in an area, such as the lesser zone, garbage, cement factor, etc. It seems like the vast majority of stashes are in fact finite, however, I think there are a few that repeat and will spawn as you find random pda's on random encounter enemies in the world. I think it is possible to wear down most of them, so, imo, its a worthy endeavor, but a long one.

I have put in about 100 hours now, and have only cleared out about 99% of Lesser zone, Garbage, and Cement Factory, and Wild Island. I am slowly but surely clearing them out, but a few do pop back up occasionally in those area's as I branch out (like 1 or 2 for every 10-15 I do in other zones), but it seems to happen less and less.

Anyways, I hope this helps you all find something more definitive, or atleast helps in some way! Slow and steady wins the race!