I'm not sure that "generations" would do it all re. ERA stopping power. Bear in mind that some modern "new-generation" ERA packs are lighter and less efficient to suit lighter vehicles.
Anyhow, I think that "generation" and "effect" variables would be redundant. Better get back to 2 variables and raise the number of "generations", each one with an upper limit of penetration/warhead size that it can stop. E.g. instead of having figures from 1 to 19, why not reaching up to 49 or 59, with more different ERA levels, from basic early-80s stuff to Kontakt-5 or similar, with several shades in between?
Just my 2c on an off-topic subject that cannot possibly be modeled in the game, I don't even know why I bothered
