You can get a rough estimate of before and afters by adding all OC TLs, good, bad, open, closed. Start from date open through today, in months. Divide by the number of TLs and convert to years.
It can also decrease if the CRA decides to delete an old account, which they do for housekeeping purposes once an account has been closed for approx. 10 years, and is thus considered by them to no longer be of value to their customers.
