God's covenants are cumulative. The new does not replace the old. God's covenants are with/applied to specific sub sets of humanity. God's covenants are either unilaterally imposed or mutually agreed to. God's covenants are either conditional or unconditional.
God's "Garden Contract" was universal and unilateral but we don't understand it. God's contract with Noah was universal and unilateral but we at least have the words of the covenant and they make (better) sense.
God's Torah/Law covenant was made with the people who came out of Egypt with Moses. It did not include the people in the Americas. It obviously could not include anyone north of the Arctic Circle.
There has only been one "everlasting covenant" (Heb. 13:20). That covenant was progressively revealed until it climaxed in the cross. That is why we read such statements like Acts 10:43; 26:21-22; Heb. 4:2; Mt. 7:13-14; Jn. 14:6; Acts 4:12; Lk. 24:24-25, 44-45; etc. that teach there has only been one gospel, one way, one savior, one salvation from Genesis to Revelation.
The "garden contract" was between God and unfallen humanity.
The righteousness of God or His holiness has always been the standard which is revealed in conscience (Rom. 2:14-15) or in human laws (Rom. 13) or in Mosaic Law and ultimately in the incarnation of Divine righteousness - Jesus Christ (Rom. 3:22) that all mankind have come short (Rom. 3:23). It is always revealed as "conditional" to demonstrate man's inability to merit the conditions.
Therefore, whatever manifestation of His glory (conscience, government, law; Christ) "no flesh" has attained to it and thus "all the world" has been condemned (Rom. 3:19-20).
Take note that Abraham is given as the example of our own justification by faith and what is a true gospel believer (Rom. 4; Gal. 3:6-8) proving that the way of salvation, the gospel, the Savior has not changed but is according to the "everlasting covenant" (Heb. 13:20).
The Mosaic law manifested both the righteousness of God in the civil administration and the salvation of God through faith in Christ in the ceremonial administration. All previous covenants contained both revelation of His righteousness and salvation in progressive forms until the cross. The conditional refers to the righteousness of God through law while the unconditional refers to the provision of the righteousness of God through Christ.
However, all sin and all salvation for the past, present and future stems from and stands on the very same fundemental basis as reported by Paul in Romans 3:24-26.
All conditional contracts serve to demonstrate and reveal the righteousness of God and how man cannot merit it.
All unconditional contracts proclaim the provision of grace through Christ that does merit it.
Hence, law and grace serve a negative and positive UNIFIED purpose working together to reveal the righteousness of God and why man cannot merit it but why it must be by promise based upon grace.