Here are the locations where I found the dates for each SSE/ETS
https://assets.pnsn.org/oldets/winter2003/
https://assets.pnsn.org/oldets/spring2004/
https://assets.pnsn.org/oldets/summer2005/
https://assets.pnsn.org/oldets/fall2006/
https://assets.pnsn.org/oldets/winter2008/
https://assets.pnsn.org/oldets/summer2009/
https://assets.pnsn.org/oldets/summer2010/
https://assets.pnsn.org/oldets/summer2011/
https://pnsn.org/tremor/tremor-log/ets-event-of-summer-2012
https://pnsn.org/tremor/tremor-log/ets-event-of-fall-2013
https://pnsn.org/tremor/tremor-log/ets-event-of-winter-2014
https://pnsn.org/tremor/tremor-log/ets-event-of-winter-201516
https://pnsn.org/tremor/tremor-log/ets-event-of-winter-2017
https://pnsn.org/tremor/tremor-log/ets-event-of-spring-2018
https://pnsn.org/blog/2019/03/29/march-2019-washington-tremor
https://pnsn.org/blog/2019/04/11/oops-correction-to-last-post
https://pnsn.org/blog/2019/04/08/when-is-an-ets-just-t
https://pnsn.org/tremor/tremor-log/ets-event-of-summer-2019
For the 1/24/2020-2/8/2020, I have not found any confirming data on the PNSN website so I emailed them. Here is my email and their reply.

