...there are only two (not three) carbons in the molecule. Thus, there appeared 2C-M, 2C-B, 2C-I, 2C-E, 2C-T and on and on.
As mentioned above, the “D” in “OD” follows from its ring orientation pattern being the same as that of 2C-D (and this, originally from the mimicking of the pattern of DOM). All of these D- compounds have the 2,5-dimethoxy-4-methyl ring-substitution pattern