Both count as D-fish, it is their roles that changed. The RV1 is being used by my Farsight forces on Pandorax. After the heavy city fighting, my Ke'lshan allies noticed ways to improve the design to match their own needs. So they built the RV2. Now both factions have a fast moving D-fish to fly in and support the Orca drop off forces on the front line. (Mental image an Orca with 2 RV's flying in support) - Perfect!
There is something about campaigns and actual battles that makes me go adaption crazy. I think you would have to have seen how many zombies that poor RV1 had to run over to truly find the inspiration for the modifications. On the other side of the coin, I really loved the look of the RV1 on the battle field so it was only a matter of time before I built another one. I have 1 Command and 1 standard D-fish for my Tau forces. 1 RV1 for my Farsight and 1 RV2 now for my Ke'lshan.
Side hobby note, there is something amazing about making all of your Septs (I am working to that goal, about 15% through them). Reading their fluff and building them to support the greater good has been a blast. There is a lot more diversity then I thought once you dive in.
Also of note, the RV2 is air caste piloted were the RV1 is AI-Drone piloted.
These are experimental adaptations for combat in the Pandorax sector. This death world is very good at killing forces that move via ground transport.
Shas'O Kais Vay Shone’nan