I joined LetterMo in 2012, and looked at InCoWriMo the following year. Over these Februarys, I have written so many letters as part of these projects, and most were not replied to. A rough count, maybe 150 surprise letters sent in February over the years. Can I remember the names of everyone I wrote to? NO, not everyone but some yes. There was a Dr. Cindy in 2015 (I don't know her surname, but she's a Canadian who was working in the NHS in the UK - I do hope she's OK, she moved around a bit...), a couple of people in Israel, one in Malta, .... memorable perhaps because of their location, and others memorable because of their name - I wrote to one person who had the same name as someone I know in my vicinity.
Many who participate in the February projects return year after year, or again later. Their names are familiar, from these projects or other postal ones. A small internet, someone elsewhere commented. Perhaps we'd crossed postal paths before, but had forgotten. So, I went through my correspondence diaries (logging in/out post). One letter I received this year was from someone I had a correspondence with in 2012 (and she did remind me of that), another letter was a reply to an InCoWriMo-reply of 2018. This year, I had what appeared to be a surprise letter, but the name was familiar, it was on my list of people I'd surprised in 2018 and had received a nice letter that month too. Had this person forgotten about our brief correspondence 3 years ago? I had! I will, of course, reply and will perhaps make fun of this, forgetting who we've both written to over the years.