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Manx Genealogy

first name 'Jo' - early 1700's

Hi All
I have an ancestor who appears in the early 1700's on Malew marriage and baptism records, by the name of Jo CORRIN (occupation weaver) Do we know if Jo is an abbreviation of another name?
I wondered about Joseph, but that doesn't repeat through our line and there were many other John Corrins, in Malew in that timeframe, so why use Jo, if he was John..This has been a puzzlement for some time.
Thankyou, Marjery