While these names are often used interchangeably in the early middle ages, I just found another stunning reminder that we need to be careful with these seemingly interchangeable medieval names! A case I just came across--three sisters who were daughters of Hildouin de Montdidier IV:
# '''Ada''' de Montdidier-Roucy, married Geoffroy, seigneur de Guise (1070 † 1141), and Gaultier d'Ath, puis à Thierry, seigneur d'Avesnes
# '''Adélaïde''' de Montdidier-Roucy (v.1035 † v.1068), married Arnoul I, († 1106), comte de Chiny.
# '''Aélis''' de Montdidier-Roucy, married Conon Falcon de La Sarraz, sire de Grandson.
They've pretty much been merged together so I'm working on separating them.
Not too creative with naming in the 11th century, were they? ;^)