I don't think it's because they're all the same make but, when I change my exhaust and, if I'm still not happy with the sound, I may consider HFC's again, just not Berks, but follow on with your thinking, it may well have to be the same manufacturer.
You probably haven't got a CEL because of them darned good Cosworths I gave you, which you cleaned, made all the difference
removing them thar scottish midges made all the difference