I just wanted to chime in my experience.

I already get Platinum Status from the Chase card. I stay at IHG properties throughout the year. A few Kimptons but mostly Staybridge, HI or HIX, rarely ICs unless I go on vacation with the family.

Signed up using the Diamond promo. Stayed 10 nights and got an email that it was extended until 2023.

I'm going to spend a total of 40 nights to claim the Lounge access benefit, the last stay is dec. 30th, to hit the 40 night for the milestone, so hopefully not an issue since it looks like room credits take a few days to post.

I stay at Staybridges, HI and HIX, so I don't see much difference in upgrades. I did stay at a CP and got a breakfast, upgrade was blah, same as platinum.

The promotion did get me to stay an extra 20 nights this year, so it worked out for IHG.

I'll probably join Ambassador since I'll stay at a few ICs in the coming year with family.