Maybe I'm a bit slow, but why should anyone protest over a serial number?
I'd rather pass out a 50-year-old VIN number than say, Social Security number or driver's license number.
I suppose there are crooks out there who can do stupid things with people's ID numbers, so a certain level of caution should be applied when personal information is asked. But sometimes it seems people get totally paranoid when it comes to giving away anything, regardless what it applies to.
I continually run into problems with my own radio customers, who don't supply an address or phone number. Uh, do you want it back? Starting January first I began asking for information WITH either a check or credit card information before I start -- with options for supplying me with the information via secure e-mail. It doesn't change a thing, it doesn't cost them an extra penny, but it has made my life a lot easier and has sliced off considerable time with turnaround for everyone. Nothing sinister, just common sense.
In the case of vintage cars, many people like to collect serial numbers for the sake of historic information -- which of course benefits everyone. Such collections provide tidbits of information, such as whether the rear view mirror is factory-correct for a certain car, when others are different. With such a collection one might find that models made in Canada with serial numbers 20056 through 20175 indeed were fitted with mirrors from a different vendor. At this very moment I'm restoring a 1924 Grebe Synchrophase radio; a VERY collectible set with numerous production changes and a very cryptic serial letter system -- yes, letters. Mine is NRFM. This one has the chain drive; it has the dampened tube sockets; it has the UX-112 output tube, etc. In the interest of providing historic information, I'm willing, and eager, to provide as much as I can.
Just my opinion.