I've got the white label as well and as far as I know it's the original mix, definitely not the same as the UK release.
I have a feeling these were done as a batch during the 80's along with a few other unreleased Motown stuff. This is assuming the labels the same as mine ink stamp with the artist and title with So Long on the flip. Think if it's got addresses and other details it may be an actual Motown test press.
Chalky may have a better idea than me, because my memory's shot