Mistranscribe not a word??

[dawnsh]

ask Susie Dent for a definitive answer

https://en.wikipedia.org/wiki/Susie_Dent

she also has a column in the Radio Times, might be worth sending her the question

[maddys52]

It probably didn't appear until lately as people had to visit archives & do their own transcriptions so there would be no mistooks  until computers became our search place 

Annie

Very true 

[Sloe Gin]

Here's the full entry for 'mistranscription' from the OED.  Earliest example is 1648, so it's not exactly recent. 

mistranscription  n.
1648   J. Goodwin Νεοϕυτοπρεσβυτερος 120   A collection of all other the untruths, falsifications, mis-transcriptions, sophistications of my words and sayings.
1854   Putnam's Monthly Mag. July 5/1   They are to be more industriously rectified and purged from the glosses and the errors of mistranscription.
1992   Rev. Eng. Stud. 43 279   There are mistranscriptions from the notoriously difficult hand of Yeats.