>How do you know if they would have believed that Christ was the promised messiah? Many jews at the
time of Christ did not believe this. Many people still don't.

What matters is what they believed at the time of their lives. This overall issue is discussed in Romans chapter 4, which explains the meaning of Genesis 15:6:

"Abram believed the LORD, and he credited it to him as righteousness."

The context is Abraham's belief in the promises of God.