There is a difference between the next available flight (which is not what they are booking you on) and the next flight with availability (which is what they are booking you on.

Yes, you can get serial bumps, but those flights were still showing availability when they booked you. They will not normally book you on a flight that does not have availability (remembering that they oversell a considerable amount of seats).

I've been bumped and told that the next flight they could get me on was three or four flights later.