I normally use mine for non-gun related stuff, or to put the factory parts back in when I change something, so for the most part they are kept.
One or two are kept empty for transport purposes, or if I have to drop something off to be worked on. Most have the serial # sticker peeled off. One or two have my name on them so my 'smith dont have to open the box to see the ticket.
I have lost a few over the years, but I dont sweat it.