So, for example, if all 6 skills are filled, does the "logic" then move on to points B and C?

Absolutely correct! For example, a level 1 hero has 3-4 free slots for new skills and abilities – and new skills will be offered to him in accordance with the percentage probability for his race. As the slots fill up, the picture changes – if there are no free slots, then no more skills will be offered (i.e., point "a" has already done its job), and offers for improvements will be made. Upon reaching the expert level, they will stop offering improvements as well (point "b"). And so on...