Piedmontese or Italian to French

According to Wikipedia the territory of Piedmont isPiedmont (Italian: Piemonte, pronounced [pjeˈmonte]; Piedmontese and Occitan: Piemont; French: Piémont). 

I have seen in French documents from the 1600's and 1700's where in French it seems to be first spelled Piemond and later on in time Pymond with double dots that is a  diaeresis (diacritic) over the "y".  This is around 1700.  Around this time it is also written as Pigmon.  In 1800 it changes again from Pimond to Pimont.  

I have read that the diaresis placed over the y could designate a vowel which is no longer present.

Are these the results of the conversions from Italian to Piemontese and then to Latin and French?