In 2011 I started keeping track of my health more, so I was able to construct a possible incomplete list of cold-symptom periods. It's possible some of them were hay fever, like Apr/May, or Sep 2019 in Australia, but I think I can tell the difference -- I had very obvious hay fever a bit later in Australia.
Oct 2010 (Paris)
Mar 2011
Dec 2011
Apr 2012
May 2013
Aug 2013
Jan 2014
Mar 2014
May 2014
Mar 2015
Jul 2015
Oct 2015
Jan 2016
Apr 2016
Jan 2017
Aug 2017
Dec 2017
Jun 2018
Sep 2018
Sep 2019
Feb 2020
2-3 episodes most years, sometimes one, and then... poof. Actually I've had a few one-day sniffles, but they never turned into "yep, that's a cold".
I wonder about the Feb 2020, which developed when I had flown to Seattle, but the symptoms didn't make me think it was anything more than a long (15+ day) cold.
See the
DW comments at
https://mindstalk.dreamwidth.org/589988.html#comments