Managing snapshots is very critical and complex topic in any environment. You should keep a track of snapshots with their creation date. You should be aware when one snapshot should be deleted, as it would be consuming space.
In this lambda script you can get consolidated report for all snapshots in your environment. I have excluded the snapshots which are copied from same or different zone. Those snapshots have volume id as vol-ffffffff. I think those should be managed separately but if you want to track those also you can simply remove the if statement from code.
You can find the script here.