In my experience, despite what the rate conditions say, it is rare that IHG hotels charge at the time of booking, or even any time BEFORE your stay.

Usually in my experience, they use the rate as a guarantee that if you don't show up then they can charge your card, but other than that, they treat it like any normal stay i.e. pre-authorise your card on check in, and charge you the final amount when you check out.

Also for a considerable amount of time I had changed card due to losing my old one, and I never updated my IHG profile. I booked all kinds of stays, both best flexible and advance purchase, and none of them ever flagged up an issue as when it came to the stay I just paid with my current card. Obviously if you didn't show up and they tried to charge you though, you would expect them to be in touch.