To make a quick comparison, I took form 2, then 4, then 1, then 3. Although Form 1 was the easiest in my opinion I still increased from form 1 to form 3, which I took a week apart at the end of studying. Just because Form 2 is easier, don't worry that you may not have improved from when you took form 3. There must be some scaling in the grading so that there is no overestimate with an "easy" form or underestimate with a "hard" form. That being said, as others and the NBME have pointed out: don't use the scores to estimate at all. But, would the NBME make all that much money if people weren't using these things to estimate??!!? I'd say you've improved and you're sure to have success. Just keep working hard until your test day. Good luck!
