OK, I've finally got to it. I pulled the rotor covers on both my unit singles. The B50 has my loose rotor fix, the B44 doesn't appear to. I tested the B50 rotor by marking it with a sharpie and then tapping on the edge of the recessed Lucas
logo in both directions to find any looseness. It is tight.
You'll notice the face of the rotor has been machined as well as the recess (the hub is also machined down flush with the aluminum) for the washer to fit. I've been riding this bike for years and letting my early 20's sons thrash on it, so that has meant lots of wheelies and trying to keep up with modern bikes. This bike was a $500.00 swap meet basket case that had thrown a rod so now it has a new liner from LA Sleeve, and a Carrillo rod and JE piston from Ed V.
Now, the B44 does not appear to be modified. There is no special washer or machining visible and I don't remember if I fitted only one washer to the back or not. The fact that the crankshaft threads don't come up flush or proud of the nut makes me think I might have. But it checks tight also.
Interestingly, the B44 with the zinc pump was not wet sumped, the B50 with the iron pump was. Go figure.
So anyway, I feel reassured that a rotor can in fact be kept together using a cupped washer strategy of some sort of pinning approach. Here are shots of an original washer and a modified washer. Notice the teeth are trimmed down to avoid digging into and damaging the aluminum
and the domed side is machined to fit the back of the nut better.
So that's my take on the whole loose rotor issue. We clearly need to check for looseness because that can lead to bad damage if neglected for too long. But, if the rotor isn't very loose, one of these methods can extend the useful life quite a lot.