So, if he goes to the screen for say crossing, but there is no crossing so its play on, but he quite clearly drops the ball over the line, then he will award the try?

Thats seems stupid to me.

That's the only thing that is agreed on when this topic is discussed with my friends. Everything else is "I'm not sure". e.g. "How far can he go back?"

We need some definitive clarification and the refs to be consistent.

my view
you should only be able to go back from when the try is scored to the play of the ball from that play.

so from the the play of the ball to the contentious try

tomkins try should have been scratched off yesterday

The debate in our house was whether the pay the ball was the last act of the previous play or the first act of the next play - ie the next play starts when the dummy half touches the ball not when the ball is played by the tackled player?

Are you going to rule out Gardners try tonight?