Your question can be answered on the basis of the last answer of Tosfos 75a DH veha'Ksiv, who writes that 2 pesukim are not required to teach that both Zav and Yoledes are allowed to eat Terumah when they become pure. The 2 Pesukim are only required in order to teach that one may eat Kodashim, which is only permitted after the Kaparah has been brought. Because it is a higher level to be able to eat Kodashim, therefore a separate Pasuk is required for each of Zav and Yoledes, because otherwise one might have said for each one that one only has to wait because it possesses a particular Chumra, i.e. "Merubeh Kaparaso" or "Hutar Michlalo". In contrast, to eat Terumah, which one may do even before acquiring a Kaparah, and which is a lower level of holiness, it is sufficient to learn from 1 Pasuk, and Zav and Yoledes can be learnt from each other.

Therefore since Tana de Bei Rebbi Yishmael (above 74b) learns that Vayikra 22:4 discusses a Zav who saw twice and a "Metzora Musgar", neither of whom require Kaparah, consequently this Pasuk is referring only to what they require in order to be allowed to eat Terumah so it follows that only 1 Pasuk is required in order to teach both the Dinim of Zav and Yoledes.

Kesivah u'Chasimah Tovah.

D. Bloom