What does it mean when the isp deletes assignment logs after

Do they only delete assignment logs of previous unique ips assigned to you? Lets say you have dynamic ip but its been the same for years, and the isp says they delete dynamic ip logs after 12 months. Does this mean the isp deletes the logs that are older than 1 year even if its the same ip? Or do they retain that information for as long as you retain the ip?

If its a dynamic ip, the isp assigns a new ip every time the lease is out, so if it renews, does this count as a new log? And will that specific assignment be kept for 12 months? Or will the timer only begin once a different ip is assigned? Or in other words, is what gets deleted the information about what ips other than your current one have previously been assigned to you? So could the isp see that ive had the same ip for several years even if they delete logs after 12 months?

Lets say the ip i currently have was first assigned to me two years ago. And from then untill now i have never had any other ip address because the same one has been renewed each time. Will the ISP keep the logs of the inital first assignment or will they only keep the metadata that it was renewed 12 months ago?

I suspect it will depend on the processes at the specific ISP. They will keep logs to assist in things like law enforcement where the police ask what user was on a particular IP address. But, what specific data they keep will likely be different across ISPs. I suspect if an IP is assigned sticky then it would have the IP and the date it was first assigned - so if that was 5 years ago then they would essentially know you had that IP for 5 years. Generally I would expect each record to show start date and end date for the assignment and if the end date is great than 12 months ago it would be purged (that is I would think the simplest way to do the history requirement).

ISPs have to comply with the law on this, much of which goes back to the RIPA Act of 2000.
https://www.legislation.gov.uk/ukpga/2000/23/contents