[Law] Conor Murray Try.

[OB..]

OB.. will probably have a better idea of this that I, but as near as I can work out, prior to 1996, the two equivalent Laws were...

LAW 18: TACKLE
LAW 19. LYING WITH, ON OR NEAR THE BALL

Some time just prior to 1996, the two Laws were combined into Law 18, and reaching out to ground the ball was allowed in either circumstance, but in the 2000 rewrite they were again separated out into Law 14 and 15 (as we know them today) and the right to reach out and score was not included in Law 14. I believe this to be an omission... it makes no sense otherwise.

Laws 18 and 19 were merged in 1986. Here is Law 19 from 1985[LAWS]LAW 19. LYING WITH, ON OR NEAR THE BALL.
(1) A player who has not been tackled but who is lying on the ground and holding the ball must immediately pass or release the ball or roll away from it or get up on his feet.
(2) A player or players lying on the ground in close proximity to the ball must not prevent an opponent gaining possession of it.
(3) A player or players from either team must not wilfully fall on or over a player who is lying on the ground with the ball in his possession or in close proximity, or on players lying on the ground with the ball between them.
(4) A player must not fall on or over the ball emerging from a scrummage or ruck.

NOTES
(i) A player on one knee or both knees or sitting on the ground is deemed to be lying on the ground.
(ii) Advantage shall be played only if it occurs immediately.
[/LAWS]

I was surprised to find (4) used to be in Law 19.

The main difference from the current Law 14 is in the detail in the Definitions section.