BB7064 retaining ring missing from Transmission?

[Lynn Eades]

Rob, I suspect you are right.
That shaft was originally made for an enclosed driveshaft set up.
The carrier gear is an adaption. As I recall the picture in the book shows some kind of tin shield as well.(that is not used in a carrier)
The bearing outer is held forward by the 6 bolt flange ring thing.
The shaft is held back by the coupling gear as you say. The thick washer sits into a rebate in the gear. I doubt it was designed to clamp against said circlip. There is ample clearance between the washer and the shaft end (without a circlip in there as well)
Leave (the one you never had) out!

That's how I see it.