A co-occurrence model isn't really meant to be used for exploration. I'm eliding a bunch of details, as it's just one of many different recommendation algorithms, and there's an exploration layer on top of the whole ensemble, which includes an epsilon-greedy component.
I may have missed the subtext/point of your earlier comment:
that the additional samples generated using the new candidate algorithm were visible to the existing algorithm, making comparison of the two algorithms difficult, and that this visibility (or its consequences) was not initially anticipated.
