The Gemoro brings a statement of Rav (first paragraph below) about the source of a law which is supported by a baraisa with the words (2nd para below) תניא נמי הכי.
Tosfos wants to know whether the תניא נמי הכי baraisa is coming to corroborate the law or the derivation.
Rav Zutra bar Tuvya says that Rav says: From where is it derived with regard to disjointed testimony, in which each of the witnesses saw the incident independent of the other, that it is not valid? It is derived from a verse, as it is stated: “He shall not die at the mouth of one witness” (Deuteronomy 17:6). The exposition is as follows: What is the meaning of “one witness”? If we say that it means one witness literally, we learn it from the first portion of the verse: “At the mouth of two witnesses,” indicating that the testimony of fewer than two witnesses is not valid. Rather, what is the meaning of “one witness”? It means that the accused is not executed based on the testimony of people who witnessed an incident with one witness here and one witness elsewhere.
The Gemara notes: תניא נמי הכי This is also taught in a baraita: It is written: “He shall not die at the mouth of one witness,” from which it is derived to include the halakha that in the case of two witnesses who observe an individual violating a capital transgression, one from this window and one from that window, and they do not see each other, that they do not join to constitute a set of witnesses. Moreover, even if they witnessed the same transgression from the same perspective, watching the incident not at the same time but one after the other in one window, they do not join to constitute a set of witnesses.
My question is whether תניא נמי הכי always comes to support one view of a preceding number of views or (as I thought until now) just to confirm the last statement being made.