Can you check the snapvault status to see if you have any stale relationships that are "locking" the snapshots?
Can you check on both the source and destination filers?
What is the snapvault schedule now?
Either way, I think you can just remove those two old snapshots manually.
There is typically one snapshot that is the baseline (snapvault locked) except when an update is happening and then you'll see two, the one being used for the update and the previous successful.
The two old snapshots are not typical. I've seen it with stale snapvault relationships, are you seeing similar snapshots from the same dates on those other volumes? Perhaps there was an issue with the vault around that time. Or, it could be that the number of weekly vault snapshots was changed - you have an active schedule of 7 daily snaps being created, if it was changed from 9 at one point, it might have not removed the two outliers properly.