If my memory serves me correct I believe one needs a starter (hv pulse) and one doesnt. I think that you are correct as to which is which. I believe that the more modern lamps are Multi Vapor and this may be why these lamps start in both fixtures.
Yes and no. All MH lamps 150W and under need a (relatively) high voltage starting pulse. MV does not. So you can put a MV lamp into a MH fixture (why you would want to, I don't know...) but if you put a <150W MH lamp into an older MV fixture, the ballast system will not have that pulse start and will fail to strike the initial arc necessary for the MH lamp. In the past, MH lamps over 150W had a different starting system and could possibly work without the pulse, but in recent years the lamp mfrs have determined that pulse start works better for all sizes and have been shifting that way. So it may have been true that in the past if you were replacing a 400W MV lamp with a 400W MH lamp it would work, but depending on the lamp that may no longer be true.
The "multi vapor" lamps that GE is selling are meant as universal donors with HPS, not MV, but mainly it is just a "marketing term" for GE's latest and greatest MH improvement. They can be used in virtually any burning position and fixture design, but it is definitely a pulse start lamp, so it ill NOT work in MV fixtures..
