Century Schoolbook - What's What?

I'm considering using Century Schoolbook for a book project and looking into the Century type family has left me a bit confused..

Whilst going through samples of different 'Century Schoolbook's in use and what's available here at school, there seems to be stark differences between some of the different Century Schoolbooks I've found. I.e. Bitstrem Century Schoolbook compared to Monotype Century Schoolbook looks very different in continuous text.

Looking around at the Typowiki and Wikpiedia page on Century didn't help either. Any information on the different 'Century Schoolbook's would be appreciated. (i.e. What was actually improved on in New Century Schoolbook if that was the cause behind the design?)