I setup a backup job for my hyper-v server, at the beginning the retention policy was 14 restore points but unfortunately i had a limitation of space in the datastore so i change it to 7 restore points from 2 days ago.
When i checked the disk backup section today i found that it keep 11 restore points instead 7.
This is normal for incremental backup mode: older backups cannot be removed until the last incremental backup in the specific full+increments chain falls out of the retention policy (otherwise, they would be unusable). Reversed incremental backup mode doesn't have this "issue", however they are slower due to additional I/O on the backup storage.
i think that i have to use the forever Forward Incremental Backup retention Policy .. to keep one full backup per week and inject the old incremental backups into the full backup.