TiVo bolt tuners

I am new to the TiVo world and had a question. I have a bolt and two minis. Today I went upstairs and tried to watch one of my minis and it said I couldn't watch live tv because all the tuners were being used. At the time my bolt was recording two shows and the other mini wasn't being watched. I thought it had 4 tuners so I should have been good....or no? Thanks