Calvin catch was a catch (he just put it down too early)... it's just the NFL wanted to crack down on letting the ball go too soon and he was in the wrong place at the wrong time and the Refs called it and made him the poster boy for the rule.
But it's simple... catch the ball in bounds and hold onto it...
For a TD... catch the ball in bounds, have it in the TD area and hold onto it...
You have to prove possession ether way... if you don't prove possession it's then a drop... it's the same all over the field.
The different is simply where you prove possession... if you prove it before the end zone all you have to do it get the ball into the end zone... if you don't prove possession before the end zone you have to prove possession in the end zone.
How long do they have to hold on to it? What is the magic point in time when the process of making a catch ends you can hit the ground and not cause an incompletion? When does going to the ground end? How long after hitting the ground does that process go?
That is the problem your simple answer doesn't address. In a perfect world, the WR holds on to the ball until after he gets up and hands it to the official. The real world isn't perfect. The rules should explain when those processes start and end. But they are so open ended, that a guy can get both feet down in bounds with control, step on the boundry, take another step, and then land on the ground losing the ball and it is incomplete. Or a guy can make a catch in the end zone, get both feet down, get his butt down, roll over onto his knees and start getting up and lose the completion because the ball squirted out of his grip after he was up on one knee.
Real examples of how poorly this rule is interpreted.
My opinion is that when the receiver controls the ball, gets 2 feet down and makes any move, the process of making a catch is over. What happens after that follows according to a ball carrier with possession. If he falls and hits the ground untouched and loses the ball, it is live. If he is knocked down, the ground can't cause a fumble and he is down by contact.
If a player touches the boundary and is touching the Football, the play is instantly dead. What happens after that is not relevant. If he had control and 2 feet or a knee in bounds the play is dead as soon as he touches the boundary. If he doesn't have control, the play is dead without that player being in possession of the ball.
If a player goes to the ground without establishing possession by the normal rules of 2 feet down and a move, then he has to control the ball and not touch the boundry or let the ball touch the ground out of his control while going to the ground.
As far as the definition of when going to the ground ends, it should be when his downward momentum stops. Even if he bounces and hits the ground a second time causing him to lose the ball. If control survived initial contact with the ground, as long as the player is in the endzone, out of bounds or downed by contact, the catch is completed and play is over. If he is not downed by contact, out ov bounds or in the end zone it is a live ball.
They need clear delineation of when those two processes start and end.
I want to go out like my Grandpa did. Peacefully in his sleep.
Not screaming in terror like his passengers.