Here is a comparison:
1A Christ foreknown before the creation of the world:
-1 Peter 1:18-20
1B Christ known before birth
-Isaiah 49:1,5
2A Individuals foreknown before the creation of the world:
(Empty set)....ahhhh not quite;
ACT 13:48
ROM 9:23
2B Individuals known before conception, or from birth, and chosen for service:
-Samson in Judges 13:5
-Jeremiah in Jer. 1:5
-John the Baptist in Luke 1:13-17
-Paul in Gal. 1:15
3A Believers in general known before the creation of the world:
-Ephesians 1:4,5,10,11,13 Paul says we were chosen in Christ before the creation of the world, but also says you were included in Christ when you heard the word of truth, the gospel of your salvation. Having believed, you were marked ....
3B Believers in general known from "the beginning"
-2 Thess 2:13,14 Here we can accept "the beginning" to be before the creation of the world, though it is not specified. But we note the individuals were called through "our gospel" and Paul's participation in the gospel, so he could call it ours, is very recent at the time of writing.
3C Believers in general foreknown
-Romans 8:29-30 Events here are spread out over time. We haven't been glorified yet.
To me 1B is the exception. This is probably due more to progressive revelation than anything else. Maybe Isaiah is setting up some possible "double fulfillments."
What you try to say about Paul could not apply to Jeremiah and Samson. I prefer to leave them sitting together in group 2B.
But what group would you put Cyrus in? Isaiah prophesied the Persian King Cyrus by name 150 years before he was born and that as a pagan, who did not know God, he would deliver the Jews to rebuild Jerusalem.
ISA 44:28 That saith of Cyrus, He is my shepherd, and shall perform all my pleasure: even saying to Jerusalem, Thou shalt be built; and to the temple, Thy foundation shall be laid.
ISA 45:1 Thus saith the LORD to his anointed, to Cyrus, whose right hand I have holden, to subdue nations before him; and I will loose the loins of kings, to open before him the two leaved gates; and the gates shall not be shut;
So it is not literally in the womb that God sets people apart, and we would be silly to say its 150 years from the womb. God knows all things from the beginning, before the foundation of the world:
ISA 46:9 ...for I am God, and there is none else; I am God, and there is none like me,
ISA 46:10 Declaring the end from the beginning, and from ancient times the things that are not yet done, saying, My counsel shall stand, and I will do all my pleasure: