The new ERRA Course for Referees

[OB..]

In fact Blue are better off as they get that much closer while green fumbles

Arguably they don't really need to be given a scrum, greens fumble brought it's own reward for blue

Only if they are so much closer as a consequence that they can impact on Green's next move - and even then they would often prefer a scrum. The referee could perhaps call Advantage.

[crossref]

Only if they are so much closer as a consequence that they can impact on Green's next move - and even then they would often prefer a scrum. The referee could perhaps call Advantage.

Under current law yes.
I was idly floating a change in the Law which would be only sanction a knock on if it advantaged the team knocking on . In this scenario green gained nothing from fumbling so play on

[OB..]

Offside is an error in judgement of law. A knock on is a error in skills.

Offside is different because the offside law specifically provides for a player not being penalised if he follows the requirements. There is no get out clause for a knock-on.