I wonder if I might have overlooked one very obvious possibility here. Given the cessation of the production of all-G/M badges in 1919 (
please note that I refer here only to those badges that were previously produced in bi-metal), and the large amount of stock which remained unused/unissued, could it be that some manufacturers simply adapted their excess all-G/M stock, by applying (in the case of the Queen's, for example) white metal scrolls directly on top of the unsupplied all-G/M badges?
This would provide one explanation as to why we see badges to regiments such as this in bi-metal, with perfectly stamped G/M sections behind the W/M scrolls.
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If the white-metal scroll were to be removed from the badge in the pictures above, it would reveal an all-G/M badge beneath (as in the example below):
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