A bit of that, too. A couple solid examples of what I’m talking about are the Long Harlequin engine article has about twice as many drawings in the original printing, and there’s an article in the reprints about a prop or a prop driven boat (I forget which) that ends abruptly mid-sentence after a half page while the original was about a seven page article.
On the other hand, as far as I can tell the Pietenpol drawings are darn close to complete if not 100% and I suspect the same of the Gere Sport. I think one of the primary gliders presented has also been built a couple times out of the FGM. The Lincoln Sport looks complete until you decide you want to start building a fuselage when it starts coming up short in a hurry. The Heath is the same way, I was going to build a rudder or something (again, I forget exactly which surface) just to hang up and there wasn’t enough detail to really even start. Given the period popularity, success, and general conformity of the Heath Parasol including scratch built ones that leads me to believe that there once was much more detail available.