The polygonal casebacks run from 53xxx into the 54xxxs for 2447s, a bit later for 3647s. Yes, I'm still refusing to call them hex backs, simply because they're not hexagonal!

Typically, the earliest watches tend to have both the poly back and Ed.Heuer signing, but there does seem to be some natural variability in there. The casebacks are leftovers from the so-called pre-Carreras. I understand the scale and speed of the Carrera's success took Heuer aback somewhat, so it's not impossible that they simply didn't have enough of the Carrera designed version in stock. Given that we are routinely seeing poly backs on low 54xxx watches, I wonder if an earlier batch made it out with the "correct" caseback before supplies ran out and they used the next best thing. Though you would expect an equivalent number of casebacks to cases.

How us your caseback signed Shaun, i.e. which version of the company name?