It's not just French/Britain. The book "How music works" describes how each country and, hell, cities, had different tunings, so an Italian singer with a perfec

It's not just French/Britain. The book "How music works" describes how each country and, hell, cities, had different tunings, so an Italian singer with a perfect pitch visiting Germany cannot really perform. Maybe just the local organ builder had a different tuning fork when building the church and everyone tuned from there :) Similar to how people didn't have standard time until relatively recently and the one clock at the town square can be off by quite a bit with the next town.