I don't want to argue with you but I am a firearms dealer in CT and as you can see on the #4473 is still listed as opitional. I think it is a PA thing.
The way it was explained to me is as follows: It used to be optional and the feds changed the regs and is no longer an option but mandatory. If this isn't correct I have to take the blame because I didn't even question it when I filled it out. Frankly, I don't really mind using it for what I feel are worthy causes, but somethings, like cell phones, internet access, etc. I feel are crossing the line.
As you can see by T_in_PA link it is a Federal law that only affects purchasing License not firearms. In CT we do not ask for SS# the State issues a list to every agent that sell Fishing, Hunting License and if a person is prohibited ( for whatever reason) from getting a license he will be on that list
That's the way it used to be(maybe still is?) in PA. I knew the federal law mandating the SSN on licenses, but was unaware of any for firearms purchases. I haven't bought a gun from a dealer in about 6 years until last Friday....I just assume they knew what was going on and let it at that....shame on me.