Hello Ed,
At the bottom of the seattube my Decade has the MM-sticker (MM6214).
Relevant I guess is the number 'in' the BB shell; that number should be model-specific. Mine is C49303.
I'm pretty sure that "C" stands for the year of production = 1992; "49" for the frame size (mine is really large); "3": I have no clue...; and "03" the serial number.
I doubt that "303" is the serial number, since not more than 30 - 50 Decades were produced. But maybe they put the MT5 and Decades together... who knows
But - that's just my estimation!