I would argue that they should. (No idea what they really do.)
Approving a generic enoxaparin is approving a very complex mixture of components each of which is biologically active. That is reason for the concern over immunogenicity. Since the characterization is taking place at the cutting edge of the relevant science, there is good reason for FDA to move forward cautiously and with an eye to how each launch goes.
There is no reason to muddy the waters and obscure possible issues by launching multiple gL's at one time.