Deleting at 80% full

So it's that time every 2 years when TiVos' hard drives are filled up with dozens of hours of content coming in a day. Due to a busy week, I'm just a little bit behind the ball with watching stuff right now, so I went from 15% to 80% in the last week. I set up the main network broadcasts to KUID, but I did not set the NBCSN, MSNBC, CNBC HD+, USA, Bravo, and Golf broadcasts to KUID, and my TiVo appears to have deleted some of them while it was at 80%. Not a huge loss, as everything in on multiple times for various rounds and stages, and I set the UConn, I mean USA Basketball games to KUID as well, but why is it doing this? I think I've read about this bizarre behaviour on here before. I would think it should get to about 97% before starting to delete things?