They are odd ducks for certain. You typically hardly ever see Chinese type 56s with dual markings like that.
Seems like from Hi/Low S/N's I have in my files, there was a fair run of at least 14000 (that is assuming that rifles in the middle of these two below were also all /416\ marked)
9428959:
9442663:
By 9454474 this arsenal stamp was gone: