I think that perhaps
Allison /
Alison is a case of two separate etymologies paralleling each other. After all, there
are people with the surname
Allison:
http://www.ancestry.com/learn/facts/fact.aspx?fid=7&ln=allison&fn= (and
http://www.ancestry.com/learn/facts/fact.aspx?&fid=10&ln=allison&fn=&yr=1920 ; though I don't know how accurate their meanings are, it seems pretty fair).
So boys called
Allison were in reference to the surname, and girls called
Allison in the -on tradition, perhaps?
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