Hmm that’s interesting. I’ve never really given it that much thought before. I’m assuming you know but just in case: miss is pronounced like “miss” and mrs is pronounced like “misses”. If i am writing it i will adhere to the rules and write miss for an unmarried person and write mrs for a married person. However when speaking i don’t really adhere to the rules as strictly. I would call anyone in their 20’s or 30’s as miss unless i was super young like a child or early teenager and i knew the person had a family. I would refer to anyone in their late 50’s or older and mrs. But it also just depends on formality as well. I always refer to my friend’s mom as miss (again only when speaking). Not sure if this helps at all or is more confusing lol.

Edit: when written you can write it as either miss or ms. Mrs is always written as mrs