Offered a set of two Omega buckles… not sure of authenticity

Dear friends,

I was offered (they said from a watchmaker dead stock) of two buckles, one in 16 mm. one in 18.mm.

I've never saw an M included in a square, and another sign that me think they are not original is the dot after ACIERINOX.

Can you let me know what you think?

Thanks a lot!