I have been reading today in the previously posted Vickers Guide AR-15 Volume 1, 2nd Edition. Page 60 & 61 discusses Armalite Prototype 000003.
The selector positions on this prototype were blanked out (note the recessed profile of each selector position) and reconfigured.


Colt LE6920 FDEC
A similar correction process is still in use by Colt as seen here in this combined image of the Armalite Prototype 000003 (top) and the Colt LE6920 FDEC (bottom) that I used to own.
