They probably all use the same latch as used on USGI M16 rifles, since that was made for the M16 and it wouldn't make sense to make it to fit another, less commonly available bayonet.
All the other US bayonets were made to fit rifles very different then the M16.
The M1 and M5-A1 was made to fit the M1 Garand, the M4 was made for the M1 Carbine, and the M6 was for the M14.
The M7 was specifically made for use on the M16 so setting up an AR15 to use one of the other bayonets would require a lot of alterations.