If injecting a non-infected animal with killed whole-cell CL bacteria is sufficient to prompt a strong enough immune response to stimulate future immunity, it makes sense that injecting an already-infected doe would probably cause the same hightened immune system reaction.
Perhaps the difference is that the infected animal would already have a whole lot more CL bacterium to fight.. And considering that pus is a byproduct of the immune system's fight against invaders, it stands to reason that kicking the immune system up against something that's already invaded might just cause there to be more pus than would be there if the immune system were just sorta lollygagging around..
So, perhaps it goes....Case-Bac = hightened immune response to CL = more pus = more knots, more quickly.