You can differ all you want but odds are they are manufacturers codes as they fit right in line with known examples, and another has actually identified them as such. What's the point of this continued argument at this point? They aren't produced by Maltby, they aren't year of manufacture. Poole did things their own way and assuming others are going to follow Poole's lead rather than traditional Britishicon marking systems is a stretch. Priest is the foremost expert on British Socket bayonets and he states, he has no knowledge of bayonet making at Maltby and the M is not associated with them. The M is associated with a dozen dispersal codes.