Of course there are new finds of stuff that's been hidden away in lofts, attics, and basements for years. But that's often just duplicates of other items that have been known for years - standard production MOCs, loose figures, etc.
But it does still amaze me in a hobby that is over 40 years old with a finite pool of items produced that there have been more than a handful of new discoveries just within the past couple years or so. The ones that come to mind immediately admittedly involve me on two of them - this is just the stuff that I am aware of. but you have:
(1) My white footer Han 12 back. First one known to have been found. Came directly from the niece of ex-Kenner salesman employee.
(2) Darrel Johnson's rocket Fett with EP box, baggy, and two rockets. First time the entire package so close to production has been found.
(3) Matt George's clear translucent DT Ben
(4) the Meccano baggy figures with the red stickers
(5) this one doesn't really count as it was already known by it's former owner, Simon Cardwell, but the only small head Han on 12/32 back
I am sure there is way more than this to the list, but these are the ones that come immediately to mind. And there is still way more stuff out there to be found. I just know it!!!!