After geting all that done, I decided to try sketching from refs & from my brain. Result: What happened to my drawing abilities?! This happens to me sometimes when I study some aspect of a process closely, so I'm reasonably sure I'll get it back. For now, I'm practicing Prokopenko's take on the Andrew Loomis style of drawing heads.
I will keep tryong to make a finished piece. In the meantime, I'm approaching my "Why isn't it working?!" Problems with more study & practice. My progress is happening fast enough that wading through this is much more pleasant than it used to be.