rear cross member plaques

[JonE]

The oblong brass plaques on the N/S of the rear cross member have come up in various threads, particularly relating to Gordon Englands. I seem to remember other mentions of these for Australia bound cars - presumably the consensus was that they pertain to rolling chassis leaving the Austin factory. But all of them?
I just wondered how widespread these were i.e. is there evidence on them on Mulliners and other coachbuilts? I'd be interested to know others, and whether owners have got evidence of the original car spec if it isn't obvious.