Here's my 0.02 Euro cts.
I have read in an article (that I cannot find anymore unfortunately) the discussion someone had with a former employee of the Omega "Bureau Technique habillement". He recalls that the original design of the Ploprof was what we now call "reversed", that is with winding crown at 3 'oclock, like a normal watch. That seems to be confirmed by the inside caseback triangular stamp of the prototypes, that was shown before.
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But apparently, the first tests showed that there were practical problems with that design: for instance, the very large crown shoulders impeded the divers left hand movements; also, when they wanted to set the time, they tried to do it with the watch still on the wrist, which sometimes resulted in pulling the whole winding stem out of the case (the ploprof owners will know what I mean
😟). I don't remember anything about handling the bezel with one hand only, but that makes sense also.
So it was immedialtely decided to reverse the watch, in order to solve these issues. That probably included the prototypes that came back for service, I imagine.
That theory - I have read the story, but I was not there at the time, so I cannot call it a fact - would explain pretty much everything, including the existence of some very early prototypes that remained in that configuration.
In addition: here's a sketch of the Ploprof case structure, taken from an Omega document. It clearly shows a watch with the winding crown on the... right:
