The intention is that bots are always ranked from 1 (Lobotomo) to 12 (Verboten). They are seeded like this after playing against each other. But in practice, some bots may fit human's style better than others and also some bots may have a different set of opponents (bot #4 will play a lot of beginners, while bot #5 even if a bit stronger will face somewhat more experienced players).
As a result, the initial correct ranking order may change over time. Sometimes, we try to rebalance it, but it is difficult to be always correct.