My mole at the College of Arms informs me that;iirc they did try to copyright the Liver birds image a few years back (their like some evil corporate conglomerate like monsanto trying to copyright human DNA) but were told where to go.That yoke on their crest is not the real Liver bird image. I think the city council retain the copyright (stand to be corrected on that).
A) The Liver Bird as a Heraldic Device...eg the City Coat of Arms, is essentially uncopyrightable...which as a result while nobody can claim it, anybody can, in theory, use it.
B) As you state, the rs only own the copy right to the cartoon version on the shirt.
C) The rights to the birds on the Liver Building still resides with the family of the sculptor / designer...but iinly for a few more years
( memo to Mr Ryazantsev; got on to that tovarisch )
D) Also, a slight tweak to the wing position would give us...if we wished a - 'Liver Bird Resurgent'
Rather fitting really.