Very interesting!
This has only ever been the case in America before, and it's used to determined the difference between Carrier sales and unlocked sim free ones.
I would imagine in this case, it means they're saying stock is available for non-iPP sales, but it could mean sim free only (so you can't reserve for a new carrier contract in store) - i'll find out after lunch for sure!
Well done for noticing. I care don't include "UNLOCKED" as a valid available status in my timeline code, so might need to adjust 🙂
Edit: Indeed, if it says "UNLOCKED" that means the store will have stock, but not for iPP. I guess they're getting ready for Saturday's standard reservation unlock.