The Lavallade family of Nerac and Bordeaux

I received an email from a member of the Lavallade family of the Angouleme/Limousin region of France, Bertrand de Lavallade, who believes that the Lavallade family of Lisburn descends from (the much earlier!) Bertrand de Lavallade of Nerac.
He told me that this family is always known as 'De Lavallade' or as 'De Lavalade' (or variations of the same) and never has a prefix such as Truffin or Chievres or St-Georges etc. etc. This rules out most of the de Lavallade families of the south-east, even the Brun de La Valade family which I had suspected Bertrand de La Vallade to be related to.   In one text, Bertrand of Nerac is referred to as Bertrand Brun de La Vallade, Sieur de Laumon - I discovered a Laumont in the district around Brive-la-Gaillard which is the area associated with the Brun de la Vallade family.  Yesterday, however, I discovered the REAL Laumond which is a townland just north of Nerac. This makes much more sense.
Moreover, Bertrand (the modern one) told me that the father of Bertrand de Lavallade was called Pierre (and not Jean as I had thought) and that this Pierre de Lavallade was also a maitre de comptes in Nerac, just like his son later.
Members of the Lavallade family of Nerac moved to live in Bordeaux;  some of these descendants were still there in the 18th century.  When I re-read the Chronicle written by Isaac Peres of Nerac in the late 16th and early 17th century, I noticed that the town of Bordeaux was endlessly mentioned, meaning that there was significant traffic between both places.   Bertrand's daughter, Catherine de Lavallade, died in Bordeaux in 1597, the year after her marriage to Jan Pinole in Nerac.   Much later, a sister of Charles de la Valade married Jacques Dubourdieu who was an elder in the church of Blaye, just north of Bordeaux, and this area is where I would expect to find the Lavallade family just prior to the Revocation.

Bertrand tells me that the Lavallade family of Nerac originated in the Languedoc - I knew that they had followed the Princes of Condé there, but was unsure of their district of origin.   He suspects that the title of Count may well have been a courtesy title, rather than an authentic title - although I personally came across a reference to 'letters of nobillity' for Bertrand de Lavallade which I will have to track down online.  Bertrand thinks that the pastor of Fontenoy-le-Comte may not have been related to Bertrand of Nerac, but several books link them together.  It is known that Pierre de La Vallade also originated in the Languedoc.

Bertrand himself descends, as I've already mentioned, from the Angoumois area, and several of his family fled France also, settling in Canterbury.  He thinks that both his family, and the family of Nerac, may have shared a common ancestry.