Just form what I can see, it appears that you are getting the general shapes right but it's lacking structure What I mean by this is that, from what I can tell, you're jumping right into the contour without establishing the structure with basic shapes. If there is no structure then this results in some of the fingers being shifted off from where they should be and the proportions being slightly off one another.
Yes I didn't use the basic shapes here. I have been having a hard time getting accurate measurements for the proportions using shapes, especially in poses where the fingers were bent or in foreshortened poses. Correct me if I'm wrong but isn't there supposed to be a point where the artist can draw hands correctly without going through the tedious process of drawing these shapes first?
Sure definetly, but they're able to skip that process because they are able to imagine those shapes in their mind after having drawn them so many times. And even then, they still use some tricks like finding the gesture of the finger tips so that they don't have to measure out each length but rather just make sure they hook up from the base of the hand to the tip.
Definitely I see an improvement in the last drawings with respect to the first, I think you should work a little volume and structure, I recommend you take a look at the book "Figure Drawing, design and invention" by Michael Hampton. I've been reading it for a few days and it has helped me to understand some concepts,
One thing I would suggest, as someone else who is on a mission to master hands, is to try drawing a few from imagination as well as observation. I've found that forces me to think about the structure of the hand rather than just transposing what's on the screen onto paper, and also helps to identify which hand positions and gestures I'm starting to get the hang of, and which need more work. When you then go back to drawing from observation you'll be able to focus in and fill in the gaps in your knowledge.