interesting, I've never seen one like the original you have there, though without wanting to be a pedant, there are at least two versions that I know of that are pre that model. One (that I have) is when the comp cut was activated by pulling up the volume knob (and it doesn't mention 'vintage' anywhere), and the earlier was in the full-drive enclosure, so a different colour.
good luck with the sale though, and definitely keep one! I'd be interested to compare your earlier model with the one I have