Some interesting things I noticed:
- the 2446 Skipper sold by Arno in the Bonhams auction had no autavia engraving on the (perfect) backcase, only a three or four small concentric semicircles at the point where you lever off the case. I asked Arno about it and he thought it was normal.
- I have seen very good condition 2446 Seafarers with a plain backcase and also with an Autavia backcase, both with the characteristic "2446 SF" stamped between the lugs. The plain one had the same marking at the detachment point
- I have seen some 2446 Autavia's with a plain back, not so sure on whether late or early models. Also with the detachment point marking.

So for me it is unsure. Makes sense that the non-Autavia models had a plain backcase, but then sense doesn't always follow in vintage watches (seamaster backcase on many speedmasters is the classic example).