They did search the OT because the NT didn't exist yet, and they searched the Septuagint (because in Thessalonika they spoke Greek), to check against St. Paul's gospel.
The Apostolic Church, on the other hand, checks the Gospels to interpret correctly St. Paul, and the rest of the New Testament, and in the light of the New Testament, the Old Testament.
So, either way, what the Protestants are proposing is backwards. I am not sure how could the Bereans check St. Paul's gospel against the OT, except for some of his quotes form that source, and some of those "quotes" are not quotes but concoctions of various verses from various books and various chapters.
It's like using words from different editions, dating back to different era, of a daily newspaper to create a "quote" that fits your teaching!
And where did they find "Christ crucified" and "saved by faith alone" in the Old Testament? Or where did they find that one does not have to follow the Law in the Old Testament? Or where did they find that the Gentiles are really "extended Israel" in the OT?
I find myself asking if you really don't know these verses or if you just hope we don't know these verses...
"Who hath believed our report? and to whom is the arm of the LORD revealed? For he shall grow up before him as a tender plant, and as a root out of a dry ground: he hath no form nor comeliness; and when we shall see him, there is no beauty that we should desire him. He is despised and rejected of men; a man of sorrows, and acquainted with grief: and we hid as it were our faces from him; he was despised, and we esteemed him not. Surely he hath borne our griefs, and carried our sorrows: yet we did esteem him stricken, smitten of God, and afflicted. But he was wounded for our transgressions, he was bruised for our iniquities: the chastisement of our peace was upon him; and with his stripes we are healed. All we like sheep have gone astray; we have turned every one to his own way; and the LORD hath laid on him the iniquity of us all. He was oppressed, and he was afflicted, yet he opened not his mouth: he is brought as a lamb to the slaughter, and as a sheep before her shearers is dumb, so he openeth not his mouth. He was taken from prison and from judgment: and who shall declare his generation? for he was cut off out of the land of the living: for the transgression of my people was he stricken. And he made his grave with the wicked, and with the rich in his death; because he had done no violence, neither was any deceit in his mouth. Yet it pleased the LORD to bruise him; he hath put him to grief: when thou shalt make his soul an offering for sin, he shall see his seed, he shall prolong his days, and the pleasure of the LORD shall prosper in his hand. He shall see of the travail of his soul, and shall be satisfied: by his knowledge shall my righteous servant justify many; for he shall bear their iniquities. Therefore will I divide him a portion with the great, and he shall divide the spoil with the strong; because he hath poured out his soul unto death: and he was numbered with the transgressors; and he bare the sin of many, and made intercession for the transgressors." -- Isaiah 53:1-12"Behold, his soul which is lifted up is not upright in him: but the just shall live by his faith." -- Habakkuk 2:4