Just to give a more encouraging counterpoint, I reached Silver at 400 tier points in March 2023. At the start of May 2023 I flew another 640 tier points and was upgraded to Gold automatically so I think the rolling red to gold upgrade period still operates in the background. It’s possible that the 800 points was being done manually which might have lead to different outcomes.

A few years ago I ended a Gold year a few points short of 1000, but I had a flight the next day which put me over the 1000. What happened was that I was downgraded to Silver as I hadn’t made the 1000, but the rolling upgrade period kicked in once the additional flight credited and I was Gold again, as the tier points still had their “up to 13 months” expiry in the background.