Coming in WAAAYYY late because this site tends to lose notifications in the chaff...

You got the lettering right. As for how I came up with this. It was ad hoc. Spur-of-the-moment inventions borne of necessity. Way back in 2013, I decided I wanted to count the total number of stories I was doing. This was way back when I was only doing so on Tumblr. The first year of challenges was an experiment, and it worked to keep my mental gears working.

So when the next year rolled around, I needed to keep track of which ones were in that year, so I stuck an A in front of the count from one to 366 [because it was a leap year of Instants because whimsy].

Since then, apart from my hardy perennial trouble with counting things, I've kept that system intact. It's honestly easier than rewiring the entire thing because I'm currently writing the 2984th daily flash fiction and redoing all of that is going to be a magnificent pain in the anatomy.