Déjà Dup .gpg backup files are significantly less than backed-up material, how to be certain it's working?

I've been using the Déjà Dup backup tool with Linux Mint for a while now and just decided to investigate whether it actually works (short of trying to restore, as I only have one machine and don't want to break it!). In snooping around, I have two questions that I was hoping someone might be able to shed light on: 1. It backs up once per week, but inside the backup location folder the last backup only has around 5 .gpg files on that date (4th April), the many many other files (490-ish .gpg files) are from other dates, with the most being from February this year... why are so few from the recent backup? Why so many (390ish) from one date in February? 2. The total size of the backup files (including all dates) is only 20.5GB (and the files from the last backup are only 176MV)... but the home directory it is supposed to be backing up is about 45GB... why so much difference? Now, I don't know much about the tool but obviously these two issues make me wonder if it's actually working... of course, maybe the files are very compressed, but why so little from the last backup and why just 176MB from these five files compared to the size of what's supposed to be backed up? If anyone can offer some clues as to why 1 and 2 might be the case (and if maybe it shouldn't be this way and maybe it isn't working!) I'd be super grateful :)