How would I know if the retailer I am purchasing from has the updated version of the walnut?
At this point, pretty much any 'new' product has to have the button updates, etc., etc., that were incorporated after initial release of TM2.
There just isn't 'New Old Stock' sitting on shelves, bc the manufacturer makes smaller runs of these (IOW, they make them by the hundreds / low thousands, versus, say, 500K run).
When the PH version came out, it was advertised as having all the v. 2.2 goodies. And that's been a couple of years ago (approx?) Couple that with tight inventory and Minimum Advertised Pricing (note sales only happen at predefined times, for very short periods)... and ANY new walnut you find from a major reseller (POTV, VG, etc.) should now be like its upgraded PH counterpart.
TL; DR: I would buy with confidence, as any *new* product should be the latest / greatest. That's been advertised for some time now, really.
PS: The enhancements, such as they were could probably be retrofitted to any existing (unshipped) product they had left in Finland. Because they were subcomponents. A couple of minutes with a Torx / screwdriver, and 'voila!' Updated version! Just hold the old stock until the new parts come in, then repackage & release to market.