I like your logic, but logic doesn't always work where Tesla are concernedI’m not saying it has anything to do with USS but the cars that are getting delivered with USS may have been sat on the Shanghai dockyard since last quarter having missed the last ship etc. The main point regarding cars not having USS is that they are definitely produced after those that do have it and therefore much more likely to have upgrades.
It could be that Tesla use the UK as the place to use up all their old stock, similar to the battery upgrades on the M3 last year where the UK only got them 3 months after every other country.
Or it could flip flop between new and old design like the rear lights which were inconsistent on UK M3s for about 6 months.
Until UK vehicles start arriving with the new rear seat it would be difficult to call what design a car will come with.