You wrote in the Background to Berachos 47b:
11a) [line 26] SIFRA - Toras Kohanim. One of the earliest commentaries on Vayikra, which was written by Rav (circa 220 C.E.) and which follows the opinion of Rebbi Yehudah.
b) [line 27] SIFRI - the commentary of Rav on Bamidbar and Devarim, which follows the opinion of Rebbi Shimon
I was taught (and everything I have seen supports) that even when it is called (She'ar) Sifr(e)i d'Vei Rav, this does not mean the Amora Rav, rather, of the Beis Midrash. I know of no source to say that Rav authored Sifri or Sifra. Throughout Shas they are considered Beraisos, and we sometimes bring them to refute Amora'im. A Stam Sifra is assumed to be Rebbi Yehudah (himself, not just according to him). And a Stam Sifri is assumed to be R. Shimon
I think that a clear proof is from the Ritva in Makos 18b, who writes that Rava is asking a question on Rav from a Beraisa even though Rav can argue on a Tana because the question is "from the Toras Kohanim, which is Sifrei d'Vei Rav..."???.
The Ritva does not say that Rava asked a contradiction in Rav. Rather, he preferred to challenge Rav from the Toras Kohanim (as opposed to others Beraisos) because it was well known.
Also, in Kidushin 53a, Abaye brought a Toras Kohanim to prove that R. Yochanan's explanation about Shitas R. Yehudah is correct, and Rav's explanation of Shitas R. Yehudah is wrong! No one discusses a contradiction in Rav, or suggests that Rav retracted from what he said in one of these 2 places.
Thank you, Pesach Feldman
(a) Our source if the Introduction of the Rambam to the Mishnah (DH u'Re'eh). The Rambam writes there that "Rav composed a Beraisa known as Sifra and Sifrei". He obviously means that Rav compiled it from various Beraisos (like Rebbi composed the Mishnah), and chose to the opinion of Rebbi Yehudah or Rebbi Shimon as the default one (See Sanhedrin 86a, an anonymous Toras Kohanim is Rebbi Yehudah and an anonymous Sifri is Rebbi Shimon), as the Tzemach David (year 979 of the fourth millenium) and Korban Aharon (in his preface) write.
The Ritva you cited, if anything, seems to support this approach. That is exactly his point when he mentions that the Toras Kohanim is also known as "Sifra d'Vei Rav."
Your point from Kidushin 53a is a good one. The answer might be that Rav is a Tana and can argue with Rebbi Yehudah (as the Ritva wrote). The Gemara is just bringing support to Rebbi Yochanan, who argues on Rav, from the opinion of Rebbi Yehudah, who also apparently argues with Rav.
(b) The Korban Aharon does cite Rashi who seems to translate the words "d'Vei Rav" differently (Chulin 61a). According to Rashi, it simply means that these Beraisos were "commonly learned in the Beis Midrash." In Gitin 67a Rashi implies that Rebbi Akiva composed the Sifra, and taught it to his student Rebbi Yehudah (who taught it to us).
Best wishes,
Mordecai Kornfeld