Pretty sure the acetate to 6x6 got an airing at the 100 Club once upon a time. It does exist but would appear to be a waste of time trying to convince you Tony.
As for unissued Motown, there's plenty that can't be found it would appear, alternate takes of Suspicion is one for a start, one which even those who have been through the vaults haven't come across, think there is at least two takes not in the public domain....or widely at least. Now I would buy that cd comp.
I still maintain that the latest offering, as good as the artists may be is only average. Some of the tracks are pleasant enough, a few are good but by and large it is an average compilation...IMHO of course. I will of course give it another listen just to confirm my beliefs. On the evidence of what I heard the other week I can wait another three years for the next one.