I heard back from HP and they told me this:
Changes are rolling out in the US first and will be rolled out subsequently in other countries.
The tracking improvement is a result of hardware changes to the physical camera module on the new Reverb G2 units. These changes are not backward compatible and are only available with the purchase of the new refreshed unit.
Software changes are compatible with all Reverb G2 headsets and customers can learn more about the updates via: https://docs.microsoft.com/en-us/windows/mixed-reality/enthusiast-guide/mixed-reality-software#windows-11-release-notes—october-2021
If customers have an issue with their cable or an issue with an AMD-based system, they may request a replacement cable for headsets under warranty through their country’s HP customer support channel. Any new cable that is sent out will be the Rev2.
The new G2 includes an all-new facemask design that enables users to adjust their eye relief distance to ensure they can better dial into their visual “sweet spot”. This new facemask now includes a removal spacer which enables users to set their eye relief distance to either 15mm (with the spacer on and as fixed on the original headset) or 9mm (with spacer off). This expanded range allows users to experience the incredible visuals the Reverb G2 has to offer.
There is more information here: https://press.hp.com/us/en/blogs/2021/award-winning-hp-reverb-g2-vr-better.html