Though England did so by way of 'Men-at-arms', professional soldiers paid by the king via a stipend to the commander or even directly. That is damn close to the company system that will rule Europe up until the second half of the 18th century.
But Westeros is no England.
The Central Authority is weak, the Magnates are strong, Trade is so-so but it clearly is not the hat of the Westerosi.
I find myself again and again reminded more of the Holy Roman Empire than of England when reading of Westeros.
I assumed a lot can be handed down, but one of the most important cost factors, the horse, cannot, actually a knight will most likely use up multiple horses in one battle, much less a lifetime. And then there is breakage, plundering of corpse and even weapons rust and decay at some point.
But still, that is why i expressed it in 'villagecattleyears'.
Westeros surely can field armored horse, in substantial amounts no doubt.
But the expenses that Manderly, who is 'only' second to third tier, would have occured, even over the years, would still have been substantial. 100 years for 100 years even with nothing getting broken, lost, etc. means that is ALL that is bought by those villages in that time.