It doesn’t take long for mold to grow on empty beer bottles. Considering beer bottles get returned for a refund, you have to assume that the brewery will make an effort to reuse as many as possible.
I toured a brewery once and they showed us the big industrial bottle washing machine. They said the bottles get scanned for cracks using a laser, and rejects obviously get tossed. The question is: what about mold, which adheres quite well to the corners of the glass? I wonder if the laser also detects bottles that didn’t get clean. Or if they just figure the temps would kill everything and just be considered safe enough from there.
Used to home-brew. Reused lots of bottles for years.
Of course, they need to be cleaned. Most brew shops sell sanitiser which will kill anything that might cause issues.