@Earnest
The 1952 RSV confirms rather than overturns the point at issue. Its main line keeps the formally exact rendering “with his own blood,” and the marginal alternative you cite—“with the blood of his Own”—does not add the word Son. It simply signals the well-known fact that τοῦ ἰδίου can be read as a possessive standing alone, exactly parallel to John 13:1 (“having loved his own”), Acts 4:23 (“to their own [people]”), and Acts 24:23 (“permit none of his own to attend upon him”). The footnote therefore preserves the same lexical surface as the text; it does not license the step that the New World Translation takes when it inserts a noun absent from every Greek witness.
The grammatical question is real, but it is limited. In Luke’s sentence the phrase διὰ τοῦ αἵματος occupies the first position in a double-attributive construction:
αἵματος | τοῦ ἰδίου
head-noun | attributive adjective in the second position
In Koine prose that pattern almost always marks simple attribution (“his own blood”). When ὁ ἴδιος functions substantivally for a cherished relative the usage is vocative or nominative and precedes the noun, it qualifies; the papyrological examples scattered through Moulton-Milligan follow that pattern and never stand after a genitive “blood.” Hebrews 13:12, written in a style indistinguishable from Luke’s, offers an exact syntactic parallel—διὰ τοῦ ἰδίου αἵματος—and no translator has ever felt impelled to supply “Son” there. Luke himself, whenever he wants to say “his own Son,” does so explicitly (Luke 9:35; Acts 3:26).
Because the syntactic default is so strong, every essentially literal version—RSV 1952, NASB, ESV, CSB, LSB, NET, NJB (2019), the Tyndale House Greek New Testament translation (2022)—prints “his own blood” in the running text. Where an edition elects the alternative, it either does so in a dynamic-equivalence setting (TEV, CEV) or flags the addition with brackets or a note, conceding that the noun is interpretive. Even the NRSV (1989) keeps the literal wording in its main line and places “his own Son” in a footnote, precisely because the editors understood that the word is not in the text.
That leads to the textual point. The possessive reading is grammatically imaginable, but it remains conjectural: no Greek manuscript—uncial, minuscule, lectionary, papyrus—contains υἱοῦ here; no version, Syriac or Coptic or Latin, translates such a word; no patristic citation includes it; and no ancient commentator says that a term was lost. Hort’s suggestion that υἱοῦ “may have slipped out” was acknowledged by Hort himself to be pure hypothesis offered to relieve what he (unlike Luke) found theologically awkward. The phenomenon he conjectured—a single-word omission in every single line of transmission—would be unique in the entire corpus of New-Testament textual history.
When translators nevertheless write “with the blood of his own Son,” they are not presenting an alternative Greek reading; they are offering an interpretive paraphrase for readers who may be unfamiliar with the idiom. That is why the RSV (1952) footnote, the NET note you quote, and the formal translations that retain the literal line all treat the possessive paraphrase as secondary and advisory, not as the text itself. The underlying scholarly judgment is unanimous across Nestle-Aland 28, UBS 5, the SBLGNT, and the Tyndale House Edition: the autograph read ἐκκλησίαν τοῦ θεοῦ … διὰ τοῦ αἵματος τοῦ ἰδίου, and the unforced reading of those words is “the church of God … with his own blood.”
Disagreement over meaning therefore cannot be projected back onto the text. Luke’s Greek is crystal-clear; what remains for the interpreter is to decide whether Luke can ascribe the shedding of that blood to “God.” The New Testament itself answers in the affirmative. In 1 Corinthians 2:8 Paul can write that the rulers “crucified the Lord of glory,” placing a divine title and a human act side-by-side. Ignatius of Antioch, a decade or two after Acts was published, speaks unself-consciously of “the blood of God” (Eph. 1:1). The idiom rests on the communicatio idiomatum, already implicit in apostolic preaching: the one person who is God the Son and the man Jesus can be described with predicates drawn from either nature.
In short, the extant Greek text of Acts 20:28 does not contain “Son,” and the grammar most naturally yields “his own blood.” All alternative renderings are post-Greek paraphrases introduced for theological or stylistic reason, not because the wording of the autograph is in doubt.