Congrats on completing the 250 box challenge!

You did well overall. I can see that your boxes have a much more consistent convergence towards their shared vanishing points towards the end of the challenge. I also see that your construction improved overall as well, your later boxes show a lot more confidence in your construction and less wobble in your lines overall.

One thing I recommend for your boxes in the future is to try and experiment with adding line weight to your boxes. This additional step will help take your boxes to the next level.

Finally while your convergences do improve overall I think this diagram will help you further develop that skill as you continue through Drawabox. So, when you are looking at your sets of lines you want to be focusing only on the lines that share a vanishing point. This does not include lines that share a corner or a plane, only lines that converge towards the same vanishing point. Now when you think of those lines, including those that have not been drawn, you can think about the angles from which they leave the vanishing point. Usually the middle lines have a small angle between them, and this angle will become negligible by the time they reach the box. This can serve as a useful hint.

You did very well overall and you clearly improved a lot. Keep in mind what I have said above and you should continue to see improvement in your construction.