I remember VMUs are supposed to hold 200 blocks for space. Well, 4 of my 5 normal sega VMUs have less than 5 blocks space left, and I needed to free up space for new saves, so I was looking at them in the bios menu...

I started counting the used blocks (from the saves) on a few of them which didn't appear to have that many saved games on them - and even though the VMU was registering as (for example) 1 block free/99% used up, the saved games were only taking up between 110-130 blocks depending on VMU.

I wound up formatting one of the VMUs, and it went back to 200 free blocks...

I was trying to think what would be doing this, and I noticed that two of the VMUs had the Skies of Arcadia logo on the VMU (if you've ever played SOA you know that it overwrites your nice VMU graphics). Could the logo somehow be taking up 40+ blocks of space? Or is it because I haven't formatted the VMUs in the last 10 or so years and doing partial deletions and saves is reducing the free memory (like a HDD that needs defragging?)?

Any ideas what causes the reduced capacity? And any ideas on how I can get back the full 200 blocks without having to wipe out all my saves? (there are some non-transferable saves, like PSO data)