Is ReadyNAS really backing up?

Hello - I have a ReadyNAS NV for which I have turned on the Time Machine Share. I have been using the share for the last 6 mos, with varying degrees of success. I have a 425GB limit set up for the share, and use it to back up two computers. Recently, both stopped backing up for reasons which were related to lack of space on the share (I forget the actual details). I started over again, removing the sparsebundles by using a trick suggested in this forum (e.g., moving the sparsebundles to a newly created share and then removing that share). I have then attempted to backup the computers again, creating a new backup for each. All seemed to be ok - the backups seemed to work fine. However, when I checked the sizes of of the backups, one was 80GB, and the other was 810MB. Looking into Preferences, I see that the estimate for the size of the complete backup is 225GB, with excluded items totaling 8.5GB. Both computers are heavily used, and in the past each backup would consume alot of space (I am not sure, but I recall the backup taking over 100GB).

What is going on? How can I diagnose what is happening?