What do you mean by this? Are you suggesting that you would not have called this a violation?

This was an obvious violation. What I mean is that once you make that signal you are obligated to make the call, there may be situations where there are circumstances that you may not want to make the call (it's similar to a preliminary on a block charge from the C or T, if you don't signal you don't have a call either way). If the violation happens early enough you can make the signal. This violation happened close enough to the release where the signal wasn't necessary.

Technically you are not obligated if the try is successful

Foul, No Violation
 

According to Rule 9.9, there is not violation because there has been no established position in the front court. All of the discussion so far appears to be that the ball is in the front court already. The jumping from the front court to the back court is not a factor because nothing has been established yet.

"in order to have a backcourt violation, “player and team” control must first be established in the frontcourt. This means a player must have been dribbling or holding the ball entirely in the frontcourt."

Isn't this a true statement? Now if his back foot lands in the newly established front court then when his front foot lands in the now defined back court it would be a violation. But in this case it would be a foul (based on the angle that I see visable)

The player's location is where he jumped from. He jumped from the FC and touched the ball in the air. Then he appears to land at least in part in the BC. That is a violation.

Peace

An airborne player retains the status of where he last touched the floor. You have frontcourt status if you jump from the frontcourt and have backcourt status once you land.

And player control is not (necessarily) required in the frontcourt to have a backcourt violation.

It's really not that complicated in this play. The Slot official missed the violation and the Lead came in with the whistle.

Player and team control had already been established, then a pass was thrown between teammates. The receiving teammate jumped from the FC (he continues to have FC status until he lands) and catches the ball. Now you have player and team control in the FC (player control in the FC is not actually required, but it's hear in this play). As soon as he lands in the BC you have a violation.

I believe the Lead did make the delayed violation call and the whistle heard in the video is his, despite the lack of a delayed violation signal.