Parent comment said: "How does one tell how often a bottle was used already?"

I don't think one can tell. How I would go about it: calculate the average number of reuse by knowing how many bottles my factory has filled and how many new bottles it needed to introduce/throw out for that. I would also sort out bottles only depending on wear and tear. As long as the bottle is good enough, reuse it one more time.

There are small bulges on the bottles which get worn away and allow making a rough estimate of uses. The german wikipedia link above has a a little bit more detailed explanation

I would assume there isn't a magic number which can't be exceeded, but something which can be observed usually happens around that time, i.e. the glass becomes visibly cloudy and it's undesirable to sell new product in them, as opposed to invisible cracks in carbon fiber composites which require ultrasound to detect.