To put the fundamental problem simply, it is your approach that is "head canon", because it is in clear conflict with onscreen facts, that is, the Star Trek universe as portrayed to us. Errors are onscreen facts, therefore real. Schemes are offscreen ideas, therefore unreal and irrelevant. They just confuse the issue, creating expectations the actual show doesn't always meet.
I'll go for the dare over the weekend, but I'll just clarify in advance that I'll be counting speaking-part guest stars rather than recycled extras (speaking or non-speaking). Although the latter present a problem of their own when the same face is associated with multiple colors of uniform...
Good point - this could be taken as supporting that this is merely an Auxiliary Control, and that the regular bridge officers are corpses somewhere on the Main Bridge.
That's a strong candidate for an explanation. OTOH, that would force us to invent an excuse for why Garrett abandoned her post up there...