You say the spot "can always be challenged." Ignoring those challenges expressly disallowed by rule, this is simply not true. To prove this argument false, one example has to be provided.

You have one example, here's another:

3rd and 1 at the 5. RB gets stood up at 5, the whistle blows. The RB, with legs churning, at the very instant the D relax their grip, runs forward past 1st down. The coach throws challenge flag and he has video evidence to prove that his RB’s most advanced progress was in EZ.

Anyone, tell me what the refs will do? If you conclude they'll proceed with the challenge; then tell me what video evidence they can look at under the hood that can change or confirm the call on the field.

Your so close to the forest you cant see the trees. The purpose of "replay" is to search for video evidence that might cause the change of a ruling on the field. If the video evidence can do nothing to affect the decision on the field: the challenge will not be allowed, the coach wont lose a TO, they'll hand the flag back to him, saying that we blew whistle on Forward progress at 5, play stopped, this was a judgement decisions that cant be reviewed. This happens a few dozen times per year.

Originally Posted by: Barfarn 

The spot can be reviewed, but I think they got the call wrong because it wasn't a GL situation so crossing the plane doesn't matter. What matters is where the ball was when the refs determined the runner's forward momentum was stopped by defenders. Since you can't tell on the replay when the whistle blew, you can't overturn the call on the field.

It's entirely possible that the refs reviewed it like a GL situation by mistake.

Originally Posted by: TedThompsonsShades 

An official shall declare the ball dead and the down ended:

(b) when a runner is held or otherwise restrained so that his forward progress ends;

The whistle just stops the play/clock.

The ball gets spotted at that furthest point where the runners momentum advanced the ball to. I can see the argument that Zeke pulled the ball back himself so that was his own momentum. But since he was being contracted by defenders officials are not going to make a determination of what backwards movement is caused by being pushed and which is caused by him pulling the ball back to tuck it away.

Where this would become tricky is say Zeke reached out with the ball like he did (19 yard line) and pulled it back the same then got pushed back to say the 21, regained his feet and moved forward again back to the 20. In that case the ball would be spotted at the 20. The ball always goes to the most forward spot even if Zeke would have been pushed back 10 yards before the whistle blew.

Originally Posted by: PackFanWithTwins 

If refs do as you say [“not going to make a determination of what backwards movement is caused by being pushed and which is caused by him pulling the ball back to tuck it away”], the play must stand as called. To assert Elliot’s FP was the 19 and NOT the 20 as called on the field, the ref must possess clear and obvious visual evidence that expressly asserts Elliot was pushed or carried backward from the 19.

That VISUAL evidence doesn’t exist.

Originally Posted by: Barfarn 

You have it all mixed up. The ruling on the field was the ball carriers forward progress was stopped and the furthest point of the ball forward only made it to the 20. The challenge was whether the ball made it further which there was clear evidence of.

Originally Posted by: PackFanWithTwins