In my opinion, the answer you seek lies more in the first video (455) than the second (495).
Firstly, your feet seemed closer to the bar in the first video than the second, I could be wrong though.
Watch the first video. The lift doesn’t get tough, the others are correct, until right about where your suppose to “pull through” and move your hips forward. But straining the hips alone does not seem enough to achieve the lift successfully.
The REASON your body doesn’t want to pull through, is because your hips beat your back on the way up. They came up to quick in proportion to your mid/upper body. You can actually see your glutes shake (No homo) at that very point, and see that the strain was on them more than anything, because of how it was awkward. pause the vid at that very moment, and look how bent over you look.
In the missed attempt, you got stuck at that point. Naturally, you actually tried to bring your ass back down and THEN complete the lift. The ass dropped before you went to put the weight down. It’s not because you tried to lean back and pull it up, it’s because the glutes were too stretched and under too much strain to pull from how high they were. You lifted it off the ground conventionally, but if you pause the video at that point, it looks like you were doing stiff (not straight) legged romanian style deadlifts.
With the way you start off your deadlift, you don’t have enough strength off your glutes or pressure on your heels. You can sit here and try these exercises to make that stronger, or you can take what your strong at and make it better. For example, if your better with your elbows tucked on the bench than spread open and wide, but when you go to bench, you tend to allow your elbows to open and your missing lifts, don’t work on benching with your elbows open, work on your form and keep your elbows in.
No offense to you other guys, and your points were valid, but it was too late for him to “pull back”. And for him to work on that would make him more well rounded, but won’t have him ready to lift by the 18th. especially if he’s trying to not only learn a new form, but strengthen it.