clarify incremental RP expiration savings and schedule-day policy-change behavior

Author: akarshprabhu

articles/backup/backup-architecture.md

@@ -140,6 +140,7 @@ Back up deduplicated disks | | | ![Partially][yellow]<br/><br/> For DPM/MABS ser
 - **Retention duration is increased / decreased:** When the retention duration is changed, the new retention duration is applied to the existing recovery points as well. As a result, some of the recovery points will be cleaned up. If the retention period is increased, the existing recovery points will have an increased retention as well.
 - **Changed from daily to weekly:** When the scheduled backups are changed from daily to weekly,  the existing daily recovery points are cleaned up.
 - **Changed from weekly to daily:** The existing weekly backups will be retained based on the number of days remaining according to the current retention policy.
+- **Schedule days/tags are changed, but retention is unchanged:** Existing recovery points continue to expire according to their current retention settings. New recovery points are no longer created for the removed schedule days/tags. Because Azure VM backup is incremental, storage reduction is gradual and depends on how much data in expired recovery points was overwritten by newer retained recovery points.
 
 ### Additional reference
 

articles/backup/manage-recovery-points.md

@@ -75,6 +75,9 @@ When the initial recovery point expires, it merges with the next incremental rec
 
 - If *Recovery Point 2* expires before *Recovery Point 1*, the data from *Recovery Point 2* is merged with the next available recovery point: *Recovery Point 3*. So block D3 is merged with *Recovery Point 3*.
 - *Recovery Point 1* is still the full backup with block D1 and D2.
+- When an in-between incremental recovery point expires, Azure Backup frees only the data blocks that are overwritten in a subsequent retained recovery point.
+- Data blocks that aren't overwritten are required to maintain the incremental chain and are carried forward (merged) into the next available retained recovery point.
+- Because of this behavior, storage reduction can be gradual and might not map 1:1 to the number of expired recovery points.
 
 ![Second case](./media/manage-recovery-points/second-case.png)