So, here’s a great example of how our brains fill in details for us.  I’ve lived in New York City for 14 years, and I have never once noticed, until a visiting friend pointed it out, that the street signs don’t have the letters after the numbers.  In other words, rather than “19th ST” or “3rd AVE”, they just say “19 ST”, “3 AVE”, etc.  Fourteen years.  Never noticed.