1 John 2:23's Overall Evidence for why 1 John 2:23b/the 2nd half of/last 10 words of 1 John 2:23 is preserved Scripture & should not in be italics but in regular text
1 John 2:23 KJB
[23] Whosoever denieth the Son, the same hath not the Father: (but) he that acknowledgeth the Son hath the Father also.

External Evidence 1 John 2:23 is part of the regular text-1 John 2:23 1598 Beza Latin Textus Receptus: Quifquis negat Filium, nec Patrem habet: qui profitetur Filium, etiam Patrem habet. 1 John 2:23 1598 Beza Greek Textus Receptus: πᾶς ὁ ἀρνούμενος τὸν υἱὸν, οὐδέ τὸν πατέρα ἔχει· ὁ ὁμολογῶν τὸν υἱὸν, καὶ τὸν πατέρα ἔχει
"Theodore Beza mentions on the Notes Page 497-498 (found on the bottom right of Page 1101 & the top of Page 1102) that "Qui profitetur...ὁ ὁμολογῶν..." (the 2nd half of 1 John 2:23), IS IN 4 codexes, in the Ancient Latin, and in the Syraic: "Qui profitetur, ὁ ὁμολογῶν,... Reftitui in Græcis hoc membrum ex quatuor manufcr.codicum, veteris Latini, & Syri interpretis aućtoritate.fic etiam affueto Ioan ne iftis oppofitionibus contrariorum vti quàm fæpiffimć.Vide Matth. 10.32." English Translation: "Who professes,...Restored in Greek, this is a
member of the four handwritten-codexes, ancient Latin, & Syrian interpreting authority. I'm Sorry Joan, I'm not going to give up on the opposite side. See also Matthew 10.32" 1598 Beza TR, Page 497-498👇 Link

Overall Manuscript Evidence for 1 John 2:23b/2nd half of 1 John 2:23 is in:
👉Cyprian (210-258AD) quoted all 1 John 2:23, including 1 John 2:23b
👉4 Greek codexes that Theodore Beza had
👉just over 70 out of 517 manuscripts having 1 John👉 Byzantine text has 1 John 2:23 in a minority yet sizable amount of Greek manuscripts
👉Old Latin 👉Complutensian Polyglot
👉Syraic 👉Armenian manuscripts 👉Aramaic-English NT 👉some Ethiopic
👉León Palimpsest
👉Codexes Floriacenis/Fleury palimpsest, Fuldensis, Ephraemi, Porphyrianus, Mosquensis I, Theodulphianus, Alexandrinus, Cavensis, Toletanus
👉Coptic
👉Extra manuscripts Psi, C, 33, 614, 630, 757, 1505, & 1739
👉Jerome's Latin Vulgate
👉wicked Critical Text & Sinaiticus
👉1452-1459:Giannozzo Manetti's New Testament on Page 151v👉1568 Bishops Bible-On 1 John 2:23b, the important thing about it is the Bishops Bible of 1568 existed BEFORE Beza's 1582, 1588, 1598 TR editions, is the 1st English Bible to mention the 2nd half of 1 John 2:23, & Bishops Bible is completely translated from Hebrew Masoretic Text & Greek Textus Receptus/TR (New Testament).
1 John 2:23 Bishops Bible 1568 which directly preceded KJB:
Whosoeuer denyeth the sonne, the same hath not the father
[But he that knowledgeth the sonne, hath the father also.]
Thus, Bishops Bible had to get tge underlined 2nd half of 1 John 2:23 from a Byzantine Greek manuscript source that existed before Beza's 1598 TR edition, or else there would not be a large 10-words half sentence in Bishops Bible
English Bishops Bible of 1568 existed before Beza 1582 TR edition but not before the previous 8 Beza TR editions, 4 Stephanus TR editions & 5 Erasmus TR editions. Beza's 1582 TR had to get 2nd half of 1 John 2:23 from a few Byzantine Greek sources [since 2nd half of 1 John 2:23 was not in the 1565 Beza TR;or else 1 John 2:23's 10-word half sentence would not exist in KJB or 1582 Beza TR]👉1556 Nuevo Testamento de Juan Perez de Pineda👉1582 TR/Textus Receptus contains all 1 John 2:23👉1588 TR👉1598 TR👉1607 Italian Diodati Bible
LINK
Internal evidence:2nd half of 1 John 2:23 should not be in italics but is part of the original text, since internally, 2nd half of 1 John 2:23 contrasts with the first half (he that denieth the Son vs he that acknowledgeth the Son; hath not the Father vs hath the Father also). 1 John 2:23b provides effective ending to verse 23 & influences verse 24's "continue in the Son, & in the Father". 2nd half of John 2:23 should not be in italics. All printers of the KJB need to unitalicize 1 John 2:23b & put it in regular words

2nd half of 1 John 2:23 is inspired, preserved, historical, biblical Scripture written by the apostle John, & should be in regular text NOT italics