Volume A - the source volume - does this have the snapshots you are trying to identify? If it has the default snapshot schedule assigned, Data OnTap will be creating the snapshots.
Volume DR_A - the destination volume - this should show the same snapshots on the source volume if it is a regular mirror, or it could have additioanl ones if it is a vault mirror.
The snapmirror relationship will also generate snapshots, that relationship can be created via Unified Manager or the CLI. You can compare the snapmirror-label to see if it matches the snapshots you are seeing.
Have you shown the volume show for both the source and destination volumes?