I was watching a documentary on the English Longbow and a big focus was the Battle of Crecy. At the end of the documentary they note how the English side lost only 2 knights while hundreds of French Knights were killed. Looking more into this claim Wikipedia lists, from different sources, causalities ranging from 1500-4000 Knights and Squires.
Now biased TV documentaries and Wikipedia sources aside, that is large amount of the Nobility class lost in a single battle much less a continuing war.
So my question is after a war costing hundreds or thousands of Squires, Knights, and other Nobility how did Europe refresh it's ranks?
Did the surviving nobility just breed their numbers back or were lower classes "promoted" into the ranks of the aristocracy?
Simon V de Montfort, lord of Montfort l'Amaury and an Earl of Leicester, child of northern French and English nobility, participant in the 4th crusades, and captain for 10 years of the crusading forces that set upon the Occitan lands in 1209, died when his head was caved in by rocks thrown by a mangonel on ramparts of Toulouse after months of siege, on June 25, 1218.
His place as leader of la croisade des Albigeois was taken by his eldest son, Amaury VI de Montfort, as well as title to the family lands in northern France. Amaury unsuccessfully lead the fight against the Saint-Gilles of Toulouse through the 1220's and lost claims to southern lands after the King of France treated with the Toulouse nobility. Amaury died while returning from subsequent crusades to the holy lands in the 1230's.
Simon's second son, Guy, was killed in the siege of Castelnaudary in 1220 while his elder brother was continuing the attempted pacification of southern lords who rebelled after Simon V's death.
Upon his death, Simon's third son, also named Simon (VI) took up the family claims to the lapsed Earldom of Leicester after his brother Amaury was unsuccessful doing so. Simon VI went on to cultivate an astonishing career in the service of, and then against, King Henry of England. He was provisional duke of the English province Gascony under Henry and then a leader of the baronial rebellions against the King of England - effectively establishing the first, if primordial, parliament in England.
None of the above describes the various other, complex chains of inheritances of blood and marriage that the Montfort's were enmeshed in and tied to: they were brothers-in-law, sisters-in-law, cousins, uncles, nephews, nieces, godsons and daughters, godfathers and mothers of other nobility and monarchy.
But it does tell us several 'typical' things about the nobility of western Europe during the high middle ages:
Nobles had many children, all of whom stood to inherit parts of their forbears' titles and properties; the above doesn't even account for their daughters Petronilla and Amicia, both of whom opted for convent life.
These children could take over or displace each other in inheritances to ensure the family line was continued.
Where there was a gap in inheritance, or better expressed as a contest of inheritance in the complex webs of intermarriage, there was always nobility ready to make claims for estates and titles.
Property and inheritance could be split and united with other estates or part thereof, and so any conception of a nobles' stable title to land is a fiction.
As for knights, they were a dime-a-dozen so to speak: knights were quite frequently impoverished, or even without lands at all due to the then-imperative to ensure continued succession of family. Many of these landless knights formed the basis of the seemingly countless mercenary armies which plagued western European countryside during the 12th through 14th centuries, and despite the protests of papacy, these same armies were hired by kings, counts or dukes themselves.
There was no need to 'refresh' nobility: there was an unending sea of nobles and knights reading to fill in the lands through any opportune crack in the dams.