Now what I'd like to discover is if LR will allow multiple files for a single camera/lens combination to evaluate different lens profiles. Can anyone save me a load of work please ?
The answer is yes.
What has tripped me up here is an undocumented feature/bug in Adobe Lens creator. If you build a profile from TIFF or JPG files the resultant lens profile won't be available to work on RAW files, ie it doesn't show up in LR at all.
(It can be edited via a text editor by changing the following line inside the profile:
Replace False by True and it works)
Preferably just build the lens profile using DNG files and there won't be a problem.
From what I can see there's no actual difference in performance between building from a TIFF and a DNG.