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Heh ... that sent me scurrying to my "Concise Oxford Dictionary". Even back when it was published (early nineties) it seems they were making an allowance for degrees of uniqueness:
2 disp. unusual, remarkable (the most unique man)
Just another example of how braindead usage can alter the meaning(s) of a word ... but at least it validates your assertion.
I'm reminded of the notion that some infinities are larger than others:
There's an infinite number of reals in the range 1..2.
There's an infinite number of reals in the range 1..3.
But there's clearly more reals in the range 1..3 than in the range 1..2 (because all of the reals in the latter also belong to the former, but not vice-versa). Therefore the infinite number of reals in the range 1..3 is greater than the infinite number of reals in the range 1..2.
If we can get people to start talking in terms of degrees of infiniteness then we'll eventually see that in the Oxford Dictionary, too, no doubt.
Anyway ... for mine something is either unique or it's not unique.