another answer:
1. you will never know until you saved each wage calculation in a table:
tblPayOut (table)
WageID (autonumber)
StaffID (number, long) 'FK to Staff table
Month (integer) ' month number
Year (integer) ' the year
Wage (currency or double or decimal)
then using Unmatched query as proposed, to know which have Staff member who's wage is not in tblPayOut:
select tblStaff.StaffID, tblStaff.StaffName From tblStaff Left Join tblPayOut
on tblStaff.StaffID = tblPayOut.StaffID
where tblPayOut.StaffID Is Null And tblPayOut.Month = theMonth And tblPayOut.Year =theYear;