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I can't pretend to be any sort of expert, but I was wondering the same thing last year and from scouring the books and internet discussions, it seems that as has been said, the 'Tiger' Zouave uniform was only really worn by one (the 'Tiger Rifles') company of one regiment for the first year of the war. An officer's letter from May 1862 describes some members of the company still wearing the uniform, but that's it.
You just had to kill the joy...