Maggie, You Asked.
The townborn names differ from the Paravian names for many reasons, and there will be differences within the town 'system' - for these reasons.
Originally, at the time of settlement, there would have been many names, from many people of MANY backgrounds and cultures - a grab bag of groups that fled the great war (interstellar empire).
When the Fellowship gave surety and swore them into the compact, they would have 'dropped out' all extra names/surnames/anything that connected them to their prior setting - and settled on ONE name for each individual/tagged to a family name 'sen' to delineate a family grouping.
This system loosely stuck - with 'sen' and a parent's name taken to denote a family group - and with time, all the various other names would have evolved or morphed - as names do, over centuries.
The clanborn took Paravian names because they had to deal with Paravians and became fluent in that language. The townborn Sen was not used - s' - became the Paravian version, and it was usually only applied to families of PROVEN lineage to interact with the Paravian races.
Some townborn names may have had origins with Earth based languages…evolved over time to an Atheran derivative.
I hope this explains your question.