US military use of "C7" style upper receivers was limited to replacement uppers used to rebuild M16A1 rifles and commercial off the shelf weapons, like the Colt RO723 M16A2 carbine, procured for certain special forces units. I'm sure plenty of M16A1 rebuilds with C7 uppers maintained the original tear drop forward assists. All the photos I've collected of the COTS M16A2 carbines used by Delta Force seem to show one of the round button variant forward assists. That's not to say maybe I just haven't seen a photo of one (in the dozens of photos I've collected), or rebuilt guns couldn't have used the tear drop style forward assist, or particular soldiers couldn't have requested it from the unit's armorers.
The tear drop forward assists do pop up on Colt M16A2 series machine guns (RO723, RO733) sold on the civilian market, though.