The transfer was legal. End of your concern.
Your friend does not recall what happened to it. This does not mean it's stolen or otherwise in bad hands. It just means that over the years it got traded away or sold or given to another person, just like you traded or sold or gave it to him. Do you honestly expect him to recall the details of every gun that's passed through his hands? The sale might be a rare and novel thing that you will recall for ages, but to some of us guns can be as individually important as baseball cards. One or two truly stand out, but the rest can be swapped back and forth with little or no emotional investment.
As for making private sales into tracked sales, well, it's not for me. It is not because I am afraid of getting on "some government list". Heck - I've been in the service, have a C&R, own NFA items of various descriptions, have or do hold carry permits from three states, am a state registered instructor in one, and am also an NRA instructor. My name is on plenty of lists. I just don't think that handing copies of my identification out to random strangers is a really good idea. I'll show my state ID and my carry permits to prove I'm legal and legit, but the moment you start copying off my information the money goes back in my wallet. I'll consider signing a very simple bill of sale, but nothing more.
And to those who are afraid that someday a cop will show up at your door asking about the one gun you sold without a receipt... relax. The ATF trace shows that you owned it once upon a time. Unless you live in some crime-free liberal mecca like CA where all transfers are required by law to be done through an FFL, not having disposition paperwork does not make you guilty of anything.
