Violation?

[Nevadaref]

MTD,
I have a problem with your definition of a throw-in pass. I do not consider the OOB pass from A1 to A2 that subsequently gets away past the sideline to be a throw-in pass. Therefore, this pass is not subject to the restrictions set forth in the throw-in rules. Specifically, the provision about having to go directly into the court does not apply to this pass.
Likewise, if we are playing in a gym with lots of room between the endline and the back wall, if A1 tried to pass the ball to A2 who was standing several feet behind A1 and the pass was missed and never touched, I do not believe that this is a violation either. Team A still has whatever time remains of the five seconds to run down the ball and release it on a throw-in pass directly into the court.
Now I do agree with your statements on where the sidelines and the endlines end. I just think that even if the ball passes the plane of the sideline while OOB the throw-in team may still retreive it and complete a throw-in pass before the five seconds expire.
I believe that we must precisely state what we consider to be BEHIND the endline, in order to discuss this play further.