AF has been tweaked based on communication between components. Hasselblad has kept the camera body firmware relatively updated on older cameras to keep pace with additional new gear. I'd assume these updates would include refinements of the AF micro-adjust system that has tweaked both speed, and more noticeably the AF accuracy.
Firmware for the H1D, H1, H2 is 9.5.0, and for the current in-production H2F it is 2.2.2 (only relevant if a CF or CFH back is used on the H2F).
This also allows use of the HTS/1.5 Adapter, HCD 35-90 Zoom lens and the DC power grip. However, of the above camera bodies, I think the HCD 28mm is only supported on the H2F camera.
Since firmware updates are only possible using the Phocus software, I do not know if updates are possible with a Phase back mounted ... I say this because the body firmware update for the H2F can only be done if you have CF or CFH sensor unit mounted. So, I'd check with Hasselblad tech support as to whether it is possible with a 3rd party back on a H1 or H2, or whether you would have to send the camera in for them to update it if possible.
The single greatest leap forward in AF performance has been the H4D with True Focus/Focus Lock. Hassey also improved the focus assist light on the H4D for lower ambient light focusing.
-Marc