Any and all combinations of tartans of the same clan are acceptable - ancient, weathered and modern, different set sizes, hunting and dress etc. However, they may not all be aesthetically pleasing!
I guess that the same general principle could be applied to tartans such as Clergy with its many variations, and to the tartans of an organisation.
Since ties and flashes are best not tartan and plaids seldom worn, that does cut down the number of combinations a bit.
It's coming yet for a' that,
That Man to Man, the world o'er,
Shall brothers be for a' that. - RB
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