Canada Post also has a canonical list of all valid addresses.
I live in an apartment, let's say unit 555 at 123 Main St, and my canonical address has the form 555-123 Main St. This is not unusual in any way.
It is vanishingly rare to find a business, software, or customer service agent that is willing to enter this address correctly, even when dealing with my provincial government or my federal government. They always want to put "Apartment" or "Unit", or move the apartment number after the street, or some other transformation.
USPS has a canonical list of all valid addresses. In most cases of hand written letters, it comes down to a human’s judgement call.