It's a good idea to check the Tapered Washer for fit on to the CV before fitting it all up. There's some tips here;-
https://www.theminif...wheel-bearings/
Like Nick, I've never used the flat washer, frankly, I see it as counter intuitive. It's fitted, torqued up, that seats all the components, then undone, so at this point, everything done prior is undone, including any seating.
The Split Tapered Washers too, I have always questioned the wisdom of. I get why they are made with the Split - to ensure that is both seats in the Taper of the Drive Flange and also over the Nose of the CV, however, as it has the Split in it, in use and especially when cornering, this Split can and does further close up, chaffing between the Drive Flange, Tapered Washer and the Wheel Bearing on the CV. If you look at a used Hub Assembly, there's evidence of this on all the parts. Some guys (Graeme C for one) have cracked and broken the Tapered Washer from flexing it in this way. If you listen when cornering hard, you can often hear this occurring, it sounds like a card being flicked by bicycle spokes.
I always had it in mind to make a set of these Tapered Washers, but without the Split, though someone one here on the Forum steered me to KAD who make these and for a sensible price. I've been running these for around a year now. The 'Card on Spokes' sound has gone. In the next few months, I'll strip my hubs down for an inspection.