The MEP program started to consolidate buying of generators during the Veitnam era, there were some models that existed prior to the MEP program that were redesignated as MEP series generators, I think the MEP-015 was one of these, maybe the MEP-016a also, although I don't recall its pre-MEP designation. I think the MEP generator designations names started around 1967, or 1968 a year or two after the MEP program was started. Too follow up on Jim's statement about the MEP-002a and MEP-003a, I am not sure about the exact introduction date, but the commonly available service manual PDF's for the MEP-003a are dated July 1977, and say they are reprints with revisions 1-4 already applied, and my MEP-002a has a 1976 date on it. As to end of production this may get a little fuzzy, I know Onan stopped building the DJE family of engines in either 1994 or 1995, however I have seen MEP-002a generators sell on GL with data plates claiming build dates as late as 2003, but builder name is listed as some odd contractor, not one of the usual suspects. My guess is these 21st century MEP-002as were build from stockpiles of spare parts, but that is just a guess.