I like the idea of labling the era alphabetically as oposed to show or series name. I guess if that is the case you would have NX, A, B, C, D, and E, what would you call Original Series era? Another way to refer to it could be similar to historical era references.
Invention (ENT: proto-Federation worlds are just aquiring the means to stretch out into the galaxy),
Exploration (TOS: five year mission are common for a century or so to boldly go. . . . Many ships lost with out a trace),
Colonial (TMP/post TMP: Inhabitants of the Federation look towards expanding to worlds to which they are not native (Genesis Device an example of this interest??), as new cultures are encountered , they join the Federation, those that don't ie. Cardassians become enemies),
Imperial (TNG: most of the Enterprise's missions included watching after and defending established Federation Territories few new planetary discoveries, borders between empires are clear and constant, Huge war over established territorites: Dominion War), . . .
Temporal (far future, time travel prevailent).
Anymore ideas?