There had been more then one or two stories about ad "not getting delivered to the target audience" and companies not noticing it through changes in sold produc

There had been more then one or two stories about ad "not getting delivered to the target audience" and companies not noticing it through changes in sold products. (Not delivered in the broad sense, from accidentally not bought over misconfigured audience to problems with ad networks.) So I'm but sure about the (micro) targeting aspects. What I'm sure about is that ads work, especially if you do them well. And it's hard to keep the quality separate from the delivery method, as you can't do clean a/b testing or similar (as things like "seen before" or even other ads can have noticable effects as far as I can tell).