Ich habe die Antwort soeben auf der schwedischen Seite von SK gefunden ...
"You are automatically upgraded to Silver or Gold membership when the required number of Basic points is registered on your account. Your personal 12-month qualification period starts with the month you enrolled in EuroBonus. For example, if you enrolled in February, the qualification period starts on February 1st and ends on January 31 of the following year. Keep in mind that benefits are effective the day you are upgraded."