I’ve reported such things before (not in a serial fashion, just been around a few years) to other manufacturers and had brutally honest replies such as “we’ve checked and it’s a bit of one of our bottles, we apologies and have implemented X and Y to ensure it doesnt happen again but sometimes things happen”.
After I had a rather unpleasant reaction to a certain brand of cough medicine (endless vomiting mainly) they requested the bottle be returned. On further checking they concluded the bottle was fine and that it’s possible I hadn’t shaken it properly and caught a particularly high dose of one of the ingredients, which was a fair assumption.
I did once get a years supply of sweets for finding some wire in a sweet – costs them virtually nothing to keep a loyal customer, if they’d sent back a letter telling me it was actually a piece of mould I’d have had a lot more to say about it.