From my research, there were:
T-26 M31 (twin MGs) = 1,626 produced (starting in 1931 - ending in 1934)
T-26 M31 (73mm + MG) = 3,631 produced (starting in 1933)
So ... EXCELLENT news that you can squeeze another MG onto the sprues so we can make either version of the twin-turret T-26. Yet another version added tot he already massive list of options!