What seems to be happening is that anaconda sees an existing label with the same name, so it appends a 1 (see fsset.py). Since I mount the old root in my PRE, think I'll now add the additional step of changing the labels so they won't conflict with the new ones anaconda wants to use. Something like the below:
This does indeed seem to be what's going on. I've added some code to clobber preexisting labels but that doesn't end up making any difference because labels are read well before the clobber code gets run. I don't yet know what the solution here is but I'll look at it again during the Rawhide cycle. - Chris