Does my 1992 400E start in first gear or second gear, some say it depends on the build date some say first some say second. I say I'm confused

Just take it out and start off normally, then quickly floor the throttle; you'll know if it shifts down quickly into a much lower gear - which would indicate it normally starts in 2nd.
Or, when stopped, you could manually pull the shifter from drive down into the lowest possible gear (usually indicated as 2nd) then return it to drive.
Then take off, the car will start in 1st gear - if this feels different from normal starts, you are normally starting in 2nd.

DG

They all start in first, but check it - watch the tach for three distinct drop-offs in RPM.