Your list isn’t entirely correct, early Model A guns had the large hole shroud, later Model A guns had small hole shrouds. My original Model A is the later small shroud and its number matching to the gun.
Not all Model B’s were green over gray, some were just green and some were green over parkerizing.
It’s also important to note that Model A guns have a fully knurled barrel nut, where as the rest have an additional band welded to the barrel nut which enlarges the locking surface for the barrel nut.