Not sure, RM.
It's one hell of a coincidence to have the same number sequence, an apparent original gun, and two different prefixes.
If the gun was assembled with these parts stateside, a fellow would need to be quite lucky to get non-refurbed parts to mate together.
And check the gas piston. It has the TM prefix, and the tube has the HM prefix.
If this is just a mis-stamped prefix or mis-assembled set of parts, it might give us insight as to the order in which parts were stamped, grouped and assembled along the line.