I have been out of the genealogy quest for a few years but just returned from France after visiting Gerardmer and Le Bresse. There are over 45 Pierrats listed in the phone books. Met the Gerardmer mayors' wife, we are related to her husband, doing research at the library. She had our families on computer dating back to the beginnings of their records to 1622. Her program does support GEDCOM. Gerardmer has a list of 22 houses there in 1522. Our families are there.
She corrected some of my dates and names. She could not speak english but could show me the correct information in the records. It was an intense 3 hours.
You can easily say all Pierrats worldwide originated there.