a session cookie establishing your authentication session only links you with the account in the system. Now, what other data is attached to that account is another thing. For example, the typical forum of yore would only have to take care of emails at best - if it doesn't have personal data, it's irrelevant, because you can't link that identity with your IRL identity.
Length of time you store the data doesn't matter, except in the sense where you can prove that effectively you do not store it at all - for example by anonymization of logs so that you do not effectively store IP addresses, even if of course they have to exist in full in the system at some point to keep the connection open.
Length of time you store the data doesn't matter, except in the sense where you can prove that effectively you do not store it at all - for example by anonymization of logs so that you do not effectively store IP addresses, even if of course they have to exist in full in the system at some point to keep the connection open.