I am reloading 358 winchester, the books say that the cases should be trimmed to 2.005". While measuring some fired brass, I found a half dozen pieces where the measurements ranged from 2.000- 2.004.
Should I discard these cases, or is it safe to reload those cases, even though they are a bit shorter than the suggested trim length?

I would go ahead and use them they will stretch in time and you can trim them then.

The Manufactures of firearms are suppose to use a standard for making the cartridge chambers and throat lengths but they all very.

Yes they're good to use but these case makers are a pain in the butt.

There is supposed to be a maximum length, manuals then recomend we trim 10thou off, and they supply anything down to 20 thou. or so short, and if we want to crimp we're expected to trim most to suit the shortest.

Not this kid, I'd rather batch them up and adjust the die. I never trim more than about 3 thou under max. as there is quite a margin over max case length before getting squeezed in the chamber.
Means measuring every reload but I batch 'em up anyway.
Stupid Lee hand/finger trimmer was taking 17 thou. off, what's the point of that??

Rule of thumb
Max length - .010 = trim to length
Trim to length - .010 = Minimum length

Make sure that you measure/trim AFTER sizing.