What are you saying, Jon, it seems you are trying to say those under the Law were saved a different way than we are under Grace?
Is that your point?
"The righteousness of God apart from the Law" is the righteousness apart from works that those under the Law were expected to do.
When they seen that they couldn't keep the Law and they were guilty of sin, the Sacrificial System was their grace and mercy.
The New Covenant in Christ is apart from the works of the Law, it's only by the grace and mercy of God, whereas under the Law god expected them to keep the Law, but gave them a way out through the Sacrificial System.
You see, Jon, we in the New Covenant are law keepers by faith in Christ who kept the Law for us.
Christ had not yet done this during the Law, they were put to the task of Keeping the Law, but given a way out through the Sacrificial System in grace and mercy.