It was considered distinct from IDW's previous "ongoing" series because it deliberately started its numbering system over with a new issue number 1. There was no obvious narrative reason for this numerical reboot, as the same TARDIS crew is used here as in the previous series. The restart came purely because IDW's main Doctor Who writer had changed from Tony Lee to Andy Diggle.
Unlike previous IDW Doctor Who titles, its indicia actually did bear a volume number. Formally, the series was called Doctor Who Volume Three.