Is it valid to suffice with the prostration of forgetfulness when basing one's decision on the lesser number of rak'ahs, without adding a rak'ah, should this occur repeatedly?

If a worshiper doubts the number of rak'ahs (units of prayer), he should base his count on the lesser number and perform the prostration of forgetfulness ( sujud al-sahw) before the taslim (salutation of peace at the end of prayer). As for someone who prayed an incorrect prayer out of ignorance of its rulings, he is not obligated to make up the past prayers. Rather, he only needs to repeat the last prayer if its time is still remaining, based on the hadith of the man who prayed incorrectly. The Prophet, peace and blessings be upon him, did not command him to make up past prayers, but only to repeat the current prayer.