I am not sure, but it is possible that some of this may be as a result of when William Caxton brought the printing press to England (as in the song which has the line "I'm the man who brought the printing press to Eng...land" to the tune of "The man who broke the bank at Monte Carlo" 
) he imported type from Europe, possibly from Cologne, so the sorts for the characters were not in the font.
This is I think why inn signs like Ye Olde Red Horse exist, because, faced with no thorn character, it was improvised with a Y.
William
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