it's simple... each person gets credits for the number of nights they are on the reservation...
in my family we have eight arriving on day one... and staying for seven nights, so each person will get seven of each type of credit (8 x 7 = 56 of each credit)
on day four we have four more people arriving... they are staying for three nights, so each person in that group will get three of each type of credit (4 x 3 = 12)
we also have one person checking in on day one, and checking out on day five, so they will have four nights and four of each type of credit (1 x 4 = 4)
each person's credits are encoded on their key to the kingdom card... guests all staying in the same room will have their credits pooled together (i.e. my mom and three nieces are staying in one room, so all four people will have their credits combined)...
it's really easier than it sounds... the number of credits follows the number of nights each individual guest is staying... with the only caveat being that each person in the same room (aka on the same ressie) have to have the same variables (number of nights)...
hope that helps clarify it a bit!