The same laws (Title 10) that cover the MOC nominations are the same for the VP. The VP can nominate up to 10 people for each of his open slots in a given year (could be 2 slots some years) and let WP decide who gets the offer. Or - just as the MOCs - he can nominate one principle with or without ranked alternates. How these VP nominations are handled can vary from year to year as the VPs and/or their assistants that handle nominations change. There are no definite statements that you can make that will always be correct. However, I know for a fact that all VP nominations do not get offers just as all MOC nominations do not get offers.