This is not strictly an NASB issue, but the name Admin, as well as the name Arni, are variants in the following Greek texts of Luke:
Nestle GNT 1904
Westcott and Hort 1881
Westcott and Hort / [NA27 variants]
and the Codex Sinaiticus
However, the textus receptus doesn't have these names in Luke, nor does the Greek Orthodox Church 1904, RP Byzantine Majority Text 2005, or the Tischendorf 8th Edition.
The NLV, ESV, BSB, BLB, CEV, ISV, NET Bible all translate this variant.
The OT source for this portion of the ancestry is Ruth 4:19 and I Chron. 2:9, which the Septuagint translated in both cases without these extra names:
So why does Matthew aways have Ram in 1:3, while Luke in certain codices have Admin and Arni in some codices, and not Ram? Perhaps the answer is found in the other sons of Hezron:
I Chron 2:18 (KJV) The sons also of Hezron, that were born unto him;
Jerahmeel, and Ram, and Chelubai.
Perhaps Arni/Armi is a corruption of Jerahmeel?
Whatever the case, the issue seems to be in the 2 generations after Hezron. Indeed, Hezron was an active progenitor:
1 Chron. 2:21-24 And afterward Hezron went in to the daughter of Machir the father of Gilead, whom he married when he was threescore years old; and she bare
him Segub. And Segub begat Jair, who had three and twenty cities in
the land of Gilead. And he took Geshur, and Aram, with the towns of
Jair, from them, with Kenath, and the towns thereof, even threescore
cities. All these belonged to the sons of Machir the father of Gilead.
And after that Hezron was dead in Calebephratah, then Abiah Hezron's
wife bare him Ashur the father of Tekoa.
So, Hezron was quite the procreator and settler in his later life. This could help explain some of the strange variations we find concerning the two generations directly after him.
So if Ram's brother gets switched in in Luke, or corruptions of Hezron's later children's names, then why doesn't Matthew have any of these variants?
I believe that Matthew was originally written in Hebrew:
Matthew also issued a written gospel among the Hebrews in their own
— Irenaeus, Against Heresies 3:1 [c.175-185 A.D.]
The first is written according to Matthew, the same that was once a
tax collector, but afterwards an emissary of Yeshua the Messiah, who
having published it for the Jewish believers, wrote it in Hebrew.
— Origen circa 210 CE, quoted by Eusebius, Eccl. Hist. 6:25
Luke however, may be originally written in Greek, as there are no such statements to suggest otherwise, and as his writing style, audience, and name suggest. Therefore, he was forced to craft his transliteration of Ruth 4 and 1 Chron. 2 (Joseph's ancestry) being a non-native speaker. The majority of Luke is eye-witness accounts, which he is brilliant at recounting. However, it is to be expected that he falls short in the area of OT Hebrew genealogy transcription/transliteration.
This is why I believe these corrupted names are found in Luke and not in Matthew.