The two dials shown above are identical (see below). So, either there was a mistake in the descriptions (implying that these are two different watches), or the dial was swapped from one watch to the other. I think that this confusion neatly illustrates how the absolute number of 35 mm tre tacches, with black (sei tacche) dials, has been made to seem larger than it really is. The same watches are getting passed around a lot.
Unfortunately, I do not think that there is a critical number of watches that, once observed, will indicate that these dials are correct. Instead, I would want to see evidence that supports the fact that convex dials are correct for these watches. Additionally, I would want to confirm that the examples we see originally had black radium dials. This may or may not be possible, depending on Longines' archive.