Edinburgh is awesome, in particular, for the way that flats can be numbered within buildings.
I used to live in flat on the top floor which received mail as either "TFL" (for top-floor, flat on the left", or "Flat 6". Different companies used different formats for the address.
I'd lived in GFL "ground-floor, flat left" and "GFR" for "Ground-floor, flat-right" as well. But never in a middle floor. I assume they would be MFL and MFR respectively. But who knows?
Flats on floors in between usually have the floor number as the first part: "3FL" for third floor on the left or "2F3" for second floor, third flat. Or at least that's how it was when I lived in Edinburgh in the 90s.
Here's a recent reddit thread on the problems of post and delivery services, and the address format for tenements. It discusses 'royal mail' vs 'council format' and the PAF
when i lived in edinburgh in the 70s, we would just stick a card on the flat door with the surnames of the inhabitants on it - the flats themselves did not have numbers.
Norwegian apartments are all identified by a single letter and four numbers. For example, H0203 means 2nd floor, 3rd apartment from the left as seen when ascending the stairs. The H means "main floors" (as opposed to the loft or cellar). Very useful when visiting other apartments.
I used to live in flat on the top floor which received mail as either "TFL" (for top-floor, flat on the left", or "Flat 6". Different companies used different formats for the address.
I'd lived in GFL "ground-floor, flat left" and "GFR" for "Ground-floor, flat-right" as well. But never in a middle floor. I assume they would be MFL and MFR respectively. But who knows?