I think "validating quality" here means "you always get the same expected quality", instead of "branded product A is better quality than unbranded product B", s

I think "validating quality" here means "you always get the same expected quality", instead of "branded product A is better quality than unbranded product B", so I'd say it still applies. In other words, unbranded cereal can, and most of the time is, better than shop brands, but that does not remove the fact that, when buying Kellogs in any shop you get exactly what you expected.