Ah ok, thank you for replies. I do remember something about a Summerset event (one where you earned a house?), but I wasn't actively playing at the time.
UESP says that one occurred in September 2018. The site also has an entry for 2020: https://en.uesp.net/wiki/Online:Events#Summerset_Celebration_2020.
There was an entry in one of the patch notes on the PTS regarding a Summerset Celebration (see https://forums.elderscrollsonline.com/en/discussion/525297/pts-patch-notes-v6-0-2) which implies there will be something soon and is presumably where UESP got their information from. I wasn't logged onto the PTS at the time so i can't say what it was like.