In the TV series Blake's 7, there were varying numbers of crew members of the Liberator and Scorpio, but never 8.
With Blake, there was Avon, Vila, Jenna, Gan and Cally. By the time Dayna, Tarrent and Soolin arrive, Blake is gone, so they are hardly 'his' 7. If you include Orac and Zen there are 7, but Orac only arrives briefly before Blake vanishes.
Is the seven referring to something other than the number of crew? Does it include Blake himself (and Zen)? Is it just a name that shouldn't be looked at too closely?