If the worshiper catches the Imam while he is bowing, when is the rak'ah counted for him?

If the latecomer joins the Imam while he is bowing, and he pronounces the Takbir while standing, then bows and settles into the position before the Imam rises, that rak'ah is counted for him; otherwise, it is not. If he doubts whether he caught it, it is not counted for him, and he performs the prostration of forgetfulness (sujud al-sahw) in the last rak'ah he performs after the Imam's salam, because he performed a rak'ah individually while doubting its increase.