Earlier quoted context omitted.
I've been looking at the domain lifecycle lately, and it can take a couple of months after the expiration date for it to actually become available for registration. I'd check with whois on the command line.
I've had my domains for decades now, and once or twice I've accidentally failed to renew in time. My registrar has a grace period during which they won't release the domain for others to register it, just to let people who accidentally let it lapse have a chance to renew it first. In my case, I failed to notice the renewal notice and only realized that I missed it once the domains stopped resolving. The grace period…
I've been working on going from calendar reminders to, at least, semi-automating checking a list of expiration dates, and then checking regularly. I'm still making mistakes, I'm just trying to avoid repeating them and instead make exciting new mistakes.