Argh, which website accounts do I have?

A few years ago my problem was how to manage the passwords of 200+ on-line accounts.

It’s gotten worse. Now I don’t remember what on-line accounts I have! Just now Paypal indicated to me that I apparently used to have a Paypal account with a certain e-mail address (that I’ve used for 10+ years). I have no recollection that I ever had such an account. Fortunately it does seem to have been closed. But what if it hadn’t been closed?

Just how am I supposed to keep track of all on-line accounts that I have over the long term? If I can’t even remember Paypal, how should I remember dozens of odd retailers from whom I ordered something once in the past almost 20 years since e-commerce became common?

All of them are potential security problems. For example, I can’t really reset any passwords on accounts that I can’t remember. And I can’t determine whether I am affected if site X is compromised, if I can’t remember whether I ever had an account there.

How do you manage this? I’m sure lost …