I definitely have been collecting for more than 30 years also, and I also rarely sell anything. I don't have receipts for things from 30 years ago, either. However, I was not buying high end branded jewelry then, either, just staple pieces like studs and random pendants, earrings, and bracelets. I have some Tiffany pieces that may not have original paperwork, but for every VCA piece I have, I have a folder for sales receipts and COAs in case I ever decide to sell or in case there was a fire and I had to prove what I owned (with digital photos). I am just saying with the super fakes out there today...as in perfect copies of VCA pieces, I wouldn't buy second hand without knowing the seller or having the original COA or receipt. The price of second hand VCA is high, and I wouldn't pay that price for a fake piece. I have a friend who bought from a reputable consignment dealer and the piece actually came with a COA that didn't match the numbers on the piece (thank goodness she checked)! That got past the authenticators at the company! (They took the item back, of course, and didn't offer it for sale again, thankfully.) We've heard other examples, as well, of VCA refusing to work on pieces (sold by these vendors who supposedly authenticate) that they can't find in their records. So to me, if the piece does not have solid authentification, then it is only worth what a reproduction would cost. On very expensive pieces or heritage pieces, obviously one can pay the $1800 to have VCA authenticate the piece.
So I do agree with your point that people who have collected a lot of branded pieces for a long time may not have had the foresight to save COAs or receipts because they never intended to sell or insure. But it doesn't change my view that it's not safe to buy without them. I only buy new from a boutique other than a couple of pieces I bought from a friend, but she also provided me the original COA and purchase receipts.