When you fill a legal form, the lines that does not apply to you shouldn't be left blank.
There are a lot of things in the instructions that aren't being followed. You don't follow every law, do you? You follow the attorney's advice if you want, or you go your own way.
You won't get denied because you left it blank or used not applicable.
N/A is a safe way to prevent someone from adding information to your application that you did not put in, leaving it blank you risk someone adding dangerous information.