I focused on those constructions because they were the examples that best demonstrated the issues for the purposes of highlighting them to you. Every submission is a body of work that provides me with a range of circumstances. I don't expect to see the same mistakes in every single piece, because not every single subject will challenge you in the same way. All I can say is that the issues I focused on came up more clearly and distinctly in the quadrupeds I focused on.

So the tricky thing about Drawabox is that it is a course that is continually adapting, changing and evolving. As I critique thousands of submissions over the course of years, I'm constantly learning how to better frame and explain concepts that have to be translated from my own somewhat ephemeral understanding. It's putting into words what a normal person who just draws for a living doesn't necessarily have to qualify - reverse engineering what I learned implicitly, so I could explain it to others. As such, approaches change, and things become more succinct over time. Unfortunately, that also means that some diagrams and demos gradually become less perfect in their representation of the particular techniques.

Until more recently, I haven't really had any opportunity to overhaul everything to bring it all back to a level of consistency - at least, not until I was able to start focusing on Drawabox on a more full-time basis. Now that I am, I'm working on a full overhaul of the course and am currently working through Lesson 1. My intent is to bring everything to what my current approach focuses upon.

Until I'm able to complete that effort, students have to deal with some demonstrations that are more up to date, and others that are less so. Students receiving official critiques are at a significant advantage, since my critiques will always reflect my most current approaches. For example, focusing on the sausage method - which does indeed focus on each sausage reflecting the characteristics of "simple" sausages (two equally sized spheres connected by a tube of consistent width, as shown in this diagram). Not all demos show its use, however, at the moment, but they're still valuable in other ways. Some demos are pretty close, but as you noted, may be a little off because when creating them, this wasn't one of my top priorities at the time.

For the additional masses, I think the different comparisons vary depending on the person. To me, a lump of soft clay is a pretty good approximation, because it's going to respond to external pressure and contact - it's not going to have depressions in it unless there is something to make them. But thinking of them more like a waterballoon may also work better. Either way, the explanation I provided in my original critique is what you'll want to focus on - where I talked about the mass wanting to stick to a simple silhouette (composed only of outward curves), and being forced to develop inward curves only when something else presses upon it.

It comes down to following strict rules about where you're allowing inward curves (complexity) and where you're sticking to outward curves (simplicity).

As to your last question, unfortunately I simply don't have the bandwidth for that. This course offers feedback as cheaply as it does, with free revisions and all, because the onus is entirely on the student to have to do a fair bit of work before they're able to receive feedback. That way when feedback is given, I am able to pick through a more substantial body of work that has a greater chance of highlighting key issues that need to be addressed - rather than going through one by one.

It may be inconvenient, but it doesn't do any harm for you to produce 5 drawings with the potential of repeating the same mistakes - aside from the time it will take to do so. Just do your best to take the feedback you've been given, and apply it to the absolute best of your ability.