Correct, but in your example, the last PTB is irrelevant as the ball has been played at by the opposition who have forced play backwards 20 metres. The tackle count has now been wiped clean and the moment the attacking player picks the ball up is essentially like the first PTB. Any metres run forward from this point are now metres gained. If the defending team pushes the attacking player back behind the point he picked the ball up, this would be metres lost.

Metres gained is surely a metric of an individual's performance with ball in hand, not a measure of how deep the attacking line sits.

so drop outs and kick offs are right then?

Yes, quite simple, the ball has been kicked by the opposition. From the moment its caught and returned, these are metres gained by the team with the ball in a brand new set of six, its no different than a team kicking on the 5th tackle and the fullback returning it.

so thats what was said at the start then, should be made from when the person gets the ball not just the advantage line

No its completely different. After a kick or charge down, there is no longer an advantage line because its a brand new set of six tackles. I'll give you that its a bit of a grey area as the player returning the ball will sometimes get easy yards but they are still metres gained in the set of six tackles. Passing the ball backwards 10 metres to a player who only runs 8 metres on the 3rd tackle is quite clearly not 8 metres gained and recording the stats in this way is quite simply crazy. You could have a player losing 2 metres from the advantage line every carry but being awarded 8 metres gained and another player that actually makes 5 metres over the advantage line every carry from flat balls and the player who lost 2 metres on every carry will have a higher metres gained stat at the end of the match.

The real number the clubs look for is metres after contact. The numbers released are inflated sometimes but its like the tackle charts, if you put your hand on as third man in then thats classed as a tackle. Once upon a time it was a tackle assist. The clubs have acess to the real numbers what matter. The ones published are a rough guide.

There's obviously some interpretation involved but I know for sure that's not how they calculate tackles, here at least.

some someone picking up a pass beats 2 men and gains 8 metres but give him a minus 2 but someone can gain 20 from a booming kick?......give over

How would he beat 2 men? In the example used, the ball is passed backwards 10 metres from the PTB. That would require the defensive line to of advanced in front of the last PTB. Ive never seen a defence that quick unless they were all stood a mile offside.

You're argument is sheer lunacy. It rewards a loss of metres forward and records it as a gain. Its like getting on the M6 Motorway at Standish, driving south 10 miles then turning around and driving back north 8 miles and saying you are 8 miles closer to Preston than you were when you started the journey. Crazy.

so you've never seen a poor pass from dummy half to a player who picks the ball up and the defence is on them?.....really?