Yep, same here. I've always been careful with applications and checking statements, so feel sure that I've never taken out PPI; although it might still be in the nature of mis-sold policies that you never noticed and never knew. So pretty difficult to be 100% certain.
I've just submitted a claim anyway, only took 5 minutes and will provide extra peace of mind when they respond. This should cover a mortgage and any other accounts opened with the same organisation. That aside, I'm not going to take speculative action for countless credit cards held over past decades as it seems impractical without a blanket way to do it.