Oly Arms sells an upper for the OA93 (ARpistol)
it says it is for "legally registerd AR15 pistol lower receivers assembled prior to  Sept 13, 1994."  What does that mean????  Well I know what assemble before Sept 13, 94 means, but "legally registered"???????

A person who bought a lower receiver in the early 1990's and built it with one of the many pistol kits, where were they to "register" it??? With the ATF? Tax Stamp??  Does that mean that any AR15 type stripped lower that was built (be it rifle or pistol) would have to also be registered???
If so - wow - there are millions of unregistered AR rifles out there???  Alot of us built the custom rifle we want.
Please help....I am obviously lost on how the proper regulations work.
I know you can't build a regular AR Pistol now without running into "crime bill" problems.  But I thought the owner of the receiver (in the early 1990's) could build a semi-pistol -(no buttstock, just a pistol grip or two)???????????????????????
thanks!