It's my understanding that often the Romanised versions were used on church documents but not in everyday life - even into the 1800s I see people being baptised as, say, Iohanna, when all of their other documents say Joan. Isn't it equally likely that families were naming the child Terence, and it was being recorded under the Latin Terentius?
https://nanowrimo.org/participants/christine-seaforth-finch
http://christineseaforthfinch.blogspot.com/