Yes, to be sure I'd buy from Lego online as early as possible. The Store online is a good fallback, as they have the same offer.Probably going to be safer to get it from the official lego website?
Part of me is considering a click and collect from a certified store, but I don't imagine they'll be guaranteeing GWPs online.
Unfortunately, the GWPs from the Store aren't available C&C. I think this is because they like to keep store stock for walk-ins (I've asked them about this before when something showed OOS in store online but was actually available in store).