In superimposed lines, I saw that many of the lines curve down in an arc, I assume they were drawn through the elbow pivot point.

In the rough perspective exercise, you used guide lines without tracing your lines. Thus, you have reduced the effect of this exercise, because you did not see where your lines actually point. https://drawabox.com/lesson/1/16/step6

We are not plotting these red lines back to the VP - just to the horizon line. This will show us a concrete idea of how far off we were.

There's a good chance that you'll find them not intersecting with it at the vanishing point, and you may also find that the further away your boxes are from the VP, the further off they are in their alignment. This is totally normal, and it helps a great deal to go over our work in this manner to help identify where our estimation of perspective tends to drift, so we know what to focus on during our next attempt.

In the tables of ellipse exercise, it was assumed that the ellipses should touch two borders, I note as an mistake that there are sections where the ellipses are made without touching two borders.

In rotated box exercise 1 i saw mistake: Not actually rotating. https://drawabox.com/lesson/1/17/notrotating

The corresponding edges of boxes are all converging towards roughly the same vanishing point. The same error can be traced in the second exercise along the horizontal axis. Perhaps because of this, you also got large gaps at the far end of the boxes.

You also didn't make good use neibouring edges to figuring out the angles of your new box edges. https://drawabox.com/lesson/1/17/step7

But overall you did a good job and I recommend starting the 250 box challenge