To answer your questions:
Sketch cards - The checklist starts with the list of artists (which in turn gives us the "card count").
If one artist did 5 sketches, and another 10, we'll add 4 and 9, respectively, to those artists' names. We will only do that for the known additional cards.
For an additions, one should submit an IR on that set's page to get the card(s) added.
Inscription set - the quantities in that Beckett article are vague and doesn't give card numbers. It is not helpful.
-- Dan --
Note: Please see my profile for more info regarding trading (section updated 3/4/2024). I have added a large portion of my inventory to the site, and currently have trading turned on (details are in my profile).