The key to these plays is understanding the "impetus" of the ball and who is responsible for that impetus.
The impeetus imparted by a player who kicks, passes, snaps, or fumbled a ball is responsible for the ball's progress even if it is defelected or reversed after striking the ground, or tougching a player of either team. So, Georgie muffed the punt--they didn't fumble--so the impetus was still ours. But, if a Georgie player had batted outside of the endzone into the endzone, that would change things.
So, to put it in english:
Georgie player muffs the kick at the three yard line. The ball rolls into the endzone. If the ball goes out of bounds, it is a touchback and Georgie retains possession. If it is inbounds, and Georgie recovers it, it is a touchback and Georgie retains possession. If GT recovers it, and the recovering player is in bounds, it is a TD. If GT recovers it but the player is out-of-bounds when doing so, it is a touch back, and Georgie retains possession.
Georgie player muffs the kick at the three yard line. The ball rolls forward and a Georgie player, attempting to prevent GT from recovering boots the ball out of the back of the endzone by kicking it. In that case, it is a safety, because the Georgie player kicked or batted the ball after it had struck the ground and changed its direction. If he just kicks it a little and it rolls into the endzone, and Georgie recovers, it would be a safety. If GT recovers, in bounds in the endzone, it is a TD. If instead of Georgie never touches the ball, no muff, and the kicked ball bounces forward, and we kick or bat the loose ball into the endzone, it is Georgie ball, a touch back, and an foul for an illegal touch.
Keep in mind that the original impetus does not change when a loose ball is batted or kicked in the endzone.
The prinicple is that until the ball hits the ground and a player changes direciton, the kicking team is responsible for the ball's impetus.
Georgie player muffs the ball in the endzone,