[Caz]

Not necessarily so. Whenever I see something about Accy Brick and the Nori sign, it usually says "legend has it" or such like.

The mould not being reversed when it was made is one - another is that the letters were simply put up in the wrong order during construction, from bottom to top.

Plus the Empire State Building is not the only well known building made from Nori, just the most famous.