Ok, so -cock is not actually from
Isaac. -cock was added on to names as a term of familiarity for men who had the "pertness of lusty and swaggering youth" (if you click the link below, scroll up a few pages to the beginning of the -cock section for this exact quote). From the same time period, there'd be nicknames like Johncock, Wilcock (
William), Peacock (
Peter).
Here's the source cited on Hitchcock:
https://www.google.com/books/edition/Curiosities_of_Puritan_Nomenclature/DiJAAAAAYAAJ?hl=en&gbpv=1&pg=PA16&printsec=frontcover
How exactly they get to Hitch from
Isaac is a bit mysterious to me (maybe
Issac ->
Yitzhak -> Hitch?), but Hitchcock could have also been a nickname for
Richard at the same time and that's more obvious (rhyming nicknames were common;
Richard ->
Rich -> Hitch -> Hitchcock).
Isadora Evander Larkin
Pax Symphorian Grey
www.behindthename.com/pnl/59411