Re: Ad's QS
An ad does not have a specific "quality score" like a keyword does, no. What ads have is "ad rank" and ad rank is what determines how well your ad does in the ad auction.
There is no published metric because ad rank varies. It can be different, depending on which of the keywords in the same Ad Group it's being triggered to serve. It can be different for the same keyword at different times, depending on what the actual search term being matched to is.
You can learn more about ad rank here - https://support.google.com/adwords/answer/1752122?hl=en
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