Did Israel or the Twelve apostles have any concept of the truths revealed to Paul?
No. Israel never had a concept of these truths, and the Twelve had no concept of them either. They were the mystery hidden in God from ages and generations, then made manifest when God revealed the secret to Saul of Tarsus, making him minister of this dispensation.
Les explains from Colossians 1:25-26 that Paul was made a minister according to the dispensation of God given to him, to fulfill or complete the Word of God. The mystery, or secret, had been hid from ages and generations and now is made manifest. Les emphasizes that all these Pauline truths were held in the mind of God. Israel never had a concept of them, and the Twelve had no concept of them either. But God saves Saul of Tarsus by grace and reveals the secrets, the mysteries, to him. That is why he was given authority to pen these epistles, which become the central part of the Scriptures, because he is the one to whom God revealed the mysteries.