For French research it begins with the Baronies and chatelaine property searches, then follow it back, cross reference with family tree websites, then department archives, then search for musters, and pay,nets for service, battle reports, ransoms, acedemia articles, casualties lists, etc. Titbits of information pulled together to form a whole picture. I have been researching this western army lead by Ambroise de Loré and Jean de Harcourt for five years now, so lots of information has been pulled together.
Cheers
Matt