I think perhaps there is no one most accurate method for all apartments.
The method you described (with so much checking and confirming) is very smart.
With apartments, though,
determining the facing gets tricky.
Sometimes it is the front door of the building... but often it is not.
Sometimes it is the entry to the apartment complex, but often not
Sometimes it is the apparent facing of the entire building but often not
Sometimes the front door of the apartment unit you live in, but most often not
Sometimes the terrace of the unit, but not necessarily.
So you take you best guess of what is the likely facing direction and creat4e charts based on that. Then you try to correlate the chart's predictions to what life in that apartment is like.
It is complicated because the floor will change the way the chart functions.
And what part of the entire floor your apartment is on will have an influence (if your unit is in the SouthEast then that will have the strongest influence)
etc.
That's why it helps to have a very good and very experienced local practitioner take a look for you.
Or else you figure it out yourself with trial and error over time
Which has always been my preferred method!