I'm from North Europe, so not a native English speaker, but still it seems like based on my experience in life it seems as the first idea is that it's Not Available.
If I was to code something and for whatever reason some data wasn't available I would use N/A.
"Not applicable" doesn't feel right to me about N/A.
For instance if there is a table of comparison and for whatever reason there is data missing for some entity, while there should be, I would use N/A. So not applicable feels wrong for me for that reason alone.
This all is coming from intuition though.