It's my understanding that there were 3 diffarent freehub bodies made for 8 speed and that the standard, Ti, and Exa-Drive cassettes are not interchangeable. Is this correct?

More importantly, how interchangeable are the rest of the 8-speed groups, i.e. will all 8-speed Ergolevers and derailieurs shift all 8-speed cassettes?

I see some hubs advertised as accepting 8,9, or 10 speed cassettes. Is this true?