Slimline tank flash rubber backing

I have often wondered if there should be a rubber backing to the slimline tank flashes, though there is nothing in the various parts manuals to suggest that there was a separate part. Whilst perusing the later model Atlas that they use as a 'reference' at Andover Norton the other day, I noticed that it had an apparently moulded backing to the tank badges it had fitted. This looked as if it was an original fit insofar as it had a flat back section with a raised 'bead' edge to surround the periphery of the tank badge so that the flash sat 'in' the backing. Further, the bead was shaped such that it was had a chamfered cross section to blend into the tank face, which would be nigh on impossible to make without tooling. The rubber was age hardened which further convinced me it was potentially original.

Can anyone advise whether this was a standard fit on all the slimline badge installations and if anyone currently supplies these backing rubbers?