Kaddish before the Amidah of Maariv when there was no quorum

A congregation began Maariv when there was no minyan in the synagogue, and the tenth person arrived after "Shomer Amo Yisrael La'ad." Can they recite the Kaddish before the Amidah?

They can recite the Kaddish before the Amidah.

The Taz in Orach Chaim, Siman 55, Se'if Katan 3, writes: "But certainly if it happened that the minyan did not come until after Ashrei, certainly for this reason the Kaddish will not be omitted, and so it is customary every day when reciting Psalms in the morning without a minyan, that they say Kaddish afterwards when a minyan arrives, and this is proper as it seems to me." However, the Magen Avraham in Siman 234, Se'if Katan 1, writes: "If Ashrei was said without a minyan and then they came to a minyan, they should say one psalm and then say Kaddish. And it seems to me that the same applies when learning in the synagogue and there is no minyan, and then ten gather to say Kaddish, it is not proper, and all the more so, since the main reason for Kaddish is the sanctification of the name, and therefore ten are needed at the time of learning, as we learn from 'And I will be sanctified among the children of Israel.' See Siman 157." The Pri Megadim in Mishbetzot Zahav, Siman 55, Se'if Katan 3, and the Mishnah Berurah there, Se'if Katan 2, cite that in Maariv, the Magen Avraham agrees with the Taz that Kaddish is said before the Amidah because it is more obligatory than Ashrei of Mincha, and therefore they can say the Kaddish.