Hi Abel, thanks a lot for this comprehensive review.
It really helps detect one from the other and will avoid some of us buying the 'wrong' ones when they are looking for the original.
Though I have no answers for the questions you ask, as I have just owned re-issue buckles, I may have found a difference in the photos you have posted:
Doesn't the font seem thicker in the original than in the re-issue 'Heuer' lettering on the outer part of the buckle?
Having said that, I must confess I am fond of these re-issue buckles: they really seem very good to me and in the real spirit of the 're-issue' in the sense of modern production of a classic with the actual feel of the original.