If a group of people assembled to pray but did not have a Minyan, and the tenth man arrived after they recited the Amida, may they recite the Hazara (repetition of the Amida) with Kedusha followed by Kaddish Titkabal? Although at this point they have a Minyan, they had already prayed the Amida without a Minyan, as individuals. The question thus arises as to whether a "Hazara" is warranted, given that the original Amida was recited as individuals, and not as part of a congregational service.
The Radbaz (Rabbi David Ben Zimra, 1480-1574) addresses this question in his work of responsa (240-241), where he rules that the group may not recite the "Hazara" in such a case. He explains that once they recited the Amida as individuals, without a Minyan, they lose the opportunity to recite the repetition of the Amida, Kedusha and Kaddish (listen to audio recording for precise citation). This is also the ruling of the Ben Ish Hai (Rabbi Yosef Haim of Baghdad, 1833-1909), in his work Rav Pe’alim (vol. 2, 26).
The Shulhan Aruch, however, rules differently, and allows a group to recite the "Hazara" with Kedusha and followed by Kaddish, even if they recited the Amida before the Minyan surfaced (Orah Haim 69:1). This is the position accepted by the Hida (Rabbi Haim Yosef David Azulai, 1724-1806), in his work Mahazik Beracha, and by the Kaf Ha’haim (Rabbi Yaakob Haim Sofer, Baghdad-Israel, 1870-1939). The Kaf Ha’haim adds that we do not apply to this case the principle of "Safek Berachot Le’hakel" (meaning, we do not recite a Beracha if its requirement is in doubt), despite the debate surrounding the issue, because of the importance of the "Hazara." The Arizal (Rabbi Yishak Luria, Israel, 1534-1572) taught that the repetition bears as much importance as the initial recitation of the Amida, and the Kaf Ha’haim therefore maintained that the group should recite the "Hazara" in this case despite the controversy involved.
Hacham Ovadia Yosef likewise follows the view of the Shulhan Aruch, and holds that the "Hazara," Kedusha and Kaddish Titkabal should be recited in such a case. He adds that even if a single individual recited the Amida privately, and then nine men arrived who had already prayed, he may repeat the Amida and recite Kedusha and Kaddish Titkabal, since a Minyan has now assembled. Even though he recited the original Amida alone, now that a Minyan has arrived he may recite the "Hazara," Kedusha and Kaddish.
Summary: If a group assembles to pray but do not have a Minyan, but after they recited the Amida a Minyan arrives, they may recite the repetition of the Amida, Kedusha and Kaddish Titkabal. This applies even if a single individual prays privately and then nine people arrive; he may repeat the Amida and recite Kedusha and Kaddish now that a Minyan is present.