I use probably 98% new, virgin, known steel, because I simply like to limit variables. But also because I like to choose compositions to suit intended use and the client's preferences; for instance one client may love a nice patina that develops over time and likes something easy to sharpen. While another may request much higher edge retention and a low-maintenance knife in general. In both cases I can recommend specific steels that fit their parameters and with which I'm familiar.
I do make file knives occasionally - thin light blades meant only for cutting and slicing, not "hard use". When I do, I make it very clear that I can't fully guarantee the HT, and leave some of the original file marks showing so there's no doubt it used to be a file. This should give some potential second or third owner a heads-up that it's a "recycled" or "repurposed" blade.
I do not entertain hypotheticals. The world as it is, is vexing enough.
Beckerhead # 350
Member, AKTI and KnifeRights