Mic: even between very early production from Cobra and later "normal release" there can be slight differences. New straps and accessories are for example not always ready for the early release so you have to do with last years stuff. I guess that if Taty had a board that had a different bottom color, it could be that the early release simply had a different color but it was decided to go with white for the main release. I remember that my early production 06 Acid 73 had the 06 graphics except for the printings on the board which where not ready so they were taken from the 05 graphics.
Such small details can be changed during the produciton run, but you can be sure the shape is the same (since its still the same mould).