Each day of the week GHQ is differens.

New girls from area 9-1 to 10-9 are in GHQ Saturday maybe on other days too.
GHQ was changed when whey interduced area 9-1 to 12-9.
All the unlocked grils should be in GHQ atleast once per week unless GHQ is bugged.

If GHQ is bugged it will be fixed soon. Don't worry you will get the girls you missed someday.