That's interesting. I have sold a LOT of vintage Gillette razors, a good amount of them were NOS and except for the 1947 boxed Super-Speed, I have zero regrets. One NOS bottle of Agua Lavanda Puig I REALLY regret selling.
A Wolf Whisker with a Black Wolf knot I traded for a Rockwell 6s that was hand polished to a mirror finish. I'm glad I got the razor as it is a favorite but don't do the long wait by my computer screen to obtain things like a WW and traded to get it. May never have another WW now unless I happen along one that strikes me in a BST.......
Honestly, I have no regrets for selling brushes. It took me a while to figure out what I liked the best and I have stuck with them for the last 7 years. (Mixed badger/boar and Semogues are my favorite) Razors on the other hand, there are a few...
I don't know maybe a Wilkinson Sticky (just plain fun) and a Gillette New Deluxe cased (that I never even tried out). That all said lately I've been thinning out my collection without any regrets.
No regrets as I haven't sold anything yet. I've given some stuff but that was fine. Now a regret I have is for Not buying a vintage complete Full seaforth set in box with lotion , talc , soap , bowl and something else I'm forgetting for less than 20 usd !!