For the Hebrew / Greek gurus
Is this phrase taken from the LXX of Gen. 48:19 (αὐτοῦ ἔσται εἰς πλῆθος ἐθνῶν) relative to (ἄχρις οὗ τὸ πλήρωμα τῶν ἐθνῶν εἰσέλθῃ) taken from Textus Receptus of Romans 11:25
BTW, I am asking. I have not a clue. Just wanted the thoughts of you all or ya'll.
I will give you my thoughts, though I am a long way from being a "Greek guru(s)"
The question would seem to be if Paul regarded a difference in the term Jew and Israel. The ancient writers seem to indicate that distinction.
For example: I am a Texan, but am also an American. When I travel (especially to a foreign land) I am distinctively from Texas, in comparison of all other regions of America. Israel included all Judea (term "Jew" derives). Yet, Jew, is considered a separate grouping. (think of a circle within a circle).
So, when one reads the writing of the ancients such as Josephus, the use of Israel is inclusive of all of the ethnic group, however, the term Jew refers to those of Judean area. Paul would make that same classic distinction.
Early on, the Jewish church struggled (being mainly Jews) with the inclusion of Gentiles, but by the end of the first century this was no longer a problem because of the majority being that of Gentiles. This (imo) in fact, was the beginnings of "replacement theology" which became the norm for the greater amount of the centuries since. Therefore, Paul's writing in Romans became realigned with a select "elect Israel" and not the ethnic grouping originally intended (imo) by Paul. And this is also why (imo) a great number of the church leadership, follow-ship and teaching from then till now holds a certain racist bias toward Israel and Israelis - but that is a completely separate issue.
A secular scholar of ancient Mediterranean writings is Jason A. Staples. He wrote a paper that has far more information on this topic and in specific the two original language quotes that you gave. I may have small areas of disagreement with what he wrote, but the documentation and explanations are solid (imo).
You may find a copy
HERE.
I am having trouble with links working, so if it doesn't, merely google "Jason A. Staples" and look for his work on "What Do the Gentiles Have to Do with “All Israel”?: A Fresh Look at Romans 11:25–27" and surely there are working links to the writing.
Trust this will give some help.