The arithmetic is the same everywhere and it is worth stating plainly. The tread is what wears out. The casing is what costs money to manufacture, and a well-treated one outlives several treads. A fleet that scraps tires at first wear-out is throwing away the expensive half every time.
Retreading reuses it. What decides how much you get back is not the retread itself but the condition the casings arrive in, which is a function of inflation discipline, repairing damage early, and not running tires flat. Fleets that pay attention to those three see more of their casings come back usable; fleets that do not send a lot of scrap.
The store you deal with can tell you what proportion of your casings is currently passing inspection, which is the number worth knowing before changing anything else.