Reconstructing Ancient Linen Body Armor - New Book

[Dan Howard]

In the "Ordinances of Louis XI" where it says: "...the best cloth that has been worn and rendered flexible being the best for this purpose..." do you think it means that these inner layers might be made of old or even discarded clothing?

Yep. There are other documents saying that old cloth is preferred.

Regulations made by the Armourers of London. 15 Edward 11. A.D. 1322. Letter-Book E. fol. cxxxiii.
That an aketon and a gambeson covered with sendale, or with cloth of silk, shall be stuffed with new cotton cloth, and with cadaz, and with old sendales, and in no other manner. And that white aketons shall be stuffed with old woven cloth, and with cotton, and made of new woven cloth within and without.
("Sendale" or "cendal" is a light, gauzy silk)

Another says that "veteran" cloth must be used.

If so, that would have lowered the cost of the armor considerably.

Yep. The trend seems to be to use old cloth on the inside layers and new, high quality cloth as the innermost and outermost layer. Some have an outermost layer of fine leather.