Keepit will retain data for a default of 12 months, but you have the possibility to individually configurable the time period.
If your retention period is 12 months, this means that each full tenant backup, which Keepit makes everyday, is retained for one year. These backups (restore points) contain copies of all data that was on your tenant at the time the backup was performed. You will have access to these restore points for 12 months from the time they were created.
So let's say you have a file that is backed up for the first time on January 1, 2019. This file is untouched until May 1, when you make some changes to it. And then finally, you decide to delete the file on June 1. This means that a copy of the original file will be retained until April 30, 2020, a copy of the changed file will be retained until May 31, and from June 1 the file will no longer be available.