Thanks for the link.
It seems you must have misread it. I saw this notice awhile ago, and it was simply letting people know that the Total Rewards website was going to finally be listing an accurate expiration date. Up until September 2019, it erroneously listed your tier expiring the upcoming January 31, even if your true expiration was to be a year later.
The rest of the notice was simply reiterating the longstanding tier policy.
Here is the relevant portion:
Notice the part I bolded.How do I continue to earn Tier Status?
The Tier Credits you earn this calendar year (January 1 – December 31, 2019) will still to count toward your Tier Status for this year and next year, expiring January 31, 2021. You need to continue earning enough Tier Credits each calendar year to maintain your Tier Status for the following year: 5,000 Tier Credits for Platinum, 15,000 Tier Credits for Diamond, and 150,000 Tier Credits to remain eligible for Seven Stars status. You are encouraged to earn the necessary thresholds each calendar year to extend your status the following year so there is no lapse in your benefits.
It's saying that, if you earned the amount for the tier this year, you will have it "the following year", as well. Just like before.
The last line, "You are encouraged to earn the necessary thresholds each calendar year to extend your status the following year so there is no lapse in your benefits" is just there to be intentionally confusing, so people don't do the "earn every 2 years" trick. But if you read it carefully, it's saying that you shouldn't under-earn in a particular year, or otherwise your status will lapse the next year. But that's always been the case.
Therefore, if you earn Diamond in 2020, it will remain Diamond for all of 2021, and will expire on 1/31/22 if you don't re-earn Diamond in 2021. There has been no change.