It's as plausible a theory as any other, Bob.
I must admit, I've changed my view of the F147 sllghtly, since my above post of 1.1.18. The dot is so perfectly symmetrical, and virtually the same size as the colon stops on the obverse (perhaps very fractionally larger), that I'm now inclined to believe it was put there deliberately. Quite possibly in the manner you suggest.