It's very easy to get lost with proportions, I'm having a similar issue with my own studies at the minute. You can see the progress as you go from drawing one through five though I've found. Which mean that the rust is being shaken off with every time you run through these exercises, and also if you look back at older attempts the progress is clear with those too.
The bottom left has a lot of character to it for sure and the lines are more confident that the rest, I'm assuming that was the last one!
All in all good work, keep at it!