It covered both, which is why I quoted both the knock-on law and the In-goal law.
No, your quotes from 1978 and 1981 all cover the scenario of the ball being knocked on INTO the in goal
1978
14 (3) Except where a try or goal is scored, if an attacking player kicks, carries, passes or knocks the ball
and it travels into his opponents' in-goal either directly or after having touched a defender who does not wilfully attempt to stop, catch, or kick it, and it is there grounded buy a player of either team, or goes into touch-in-goal or over the dead ball line a drop out shall be awarded.
17 Note (3) If an attacking player
knocks-on in the field of play and the ball travels into in-goal either directly or after having touched a defender who does not wilfully attempt to stop, catch, or kick it, and it is there grounded by a player of either team, or goes into touch-in-goal or over the dead ball line a drop out shall be awarded.
1981
14 (3) Except where the ball is knocked on or thrown forward or if an attacking player kicks, carries or passes the ball a
nd it travels into his opponents' in-goal either directly or after having touched a defender who does not wilfully attempt to stop, catch, or kick it, and it is there grounded buy a player of either team, or goes into touch-in-goal or over the dead ball line a drop out shall be awarded.
17 Note (iii) if an attacking player kicks, carries, passes or knocks the ball a
nd it travels into his opponents' in-goal either directly or after having touched a defender who does not wilfully attempt to stop, catch, or kick it, and it is there grounded buy a player of either team, or goes into touch-in-goal or over the dead ball line, a scrummage should be awarded at the place of the knock-on or throw-forward.