The Pauline letters clearly distinguish between God and the Lord. This distinction exists within the Jewish scriptures, and was very likely something understood by many Jews and a God-fearers.
In much the same way that Philo distinguishes between God and his son the Word, the Pauline letters appear to distinguish between God and the Lord.
If we take an example:
Original:
1 Paul, called to be an apostle of Christ Jesus by the will of God, and our brother Sosthenes,
2 To the church of God in Corinth, to those sanctified in Christ Jesus and called to be his holy people, together with all those everywhere who call on the name of our Lord Jesus Christ—their Lord and ours:
3 Grace and peace to you from God our Father and the Lord Jesus Christ.
4 I always thank my God for you because of his grace given you in Christ Jesus. 5 For in him you have been enriched in every way—with all kinds of speech and with all knowledge— 6 God thus confirming our testimony about Christ among you. 7 Therefore you do not lack any spiritual gift as you eagerly wait for our Lord Jesus Christ to be revealed. 8 He will also keep you firm to the end, so that you will be blameless on the day of our Lord Jesus Christ. 9 God is faithful, who has called you into fellowship with his Son, Jesus Christ our Lord.
Revised
1 Paul, called to be an apostle of Christ by the will of God, and our brother Sosthenes,
2 To the church of God in Corinth, to those sanctified in Christ and called to be his holy people, together with all those everywhere who call on the name of our Lord Christ—their Lord and ours:
3 Grace and peace to you from God our Father and the Lord Christ.
4 I always thank my God for you because of his grace given you in Christ. 5 For in him you have been enriched in every way—with all kinds of speech and with all knowledge— 6 God thus confirming our testimony about Christ among you. 7 Therefore you do not lack any spiritual gift as you eagerly wait for our Lord Christ to be revealed. 8 He will also keep you firm to the end, so that you will be blameless on the day of our Lord Christ. 9 God is faithful, who has called you into fellowship with his Son, Christ our Lord.
Obviously, v2 says, "who call on the name of our Lord". Christ isn't a name. This is an example of a verse that may not make sense without the name Jesus present.
Then again, maybe the name was supposed to be unstated in writing? Also, maybe v2 is a later revision?
In Vision of Isaiah the name Jesus is also not used, instead using the term the Beloved, who is the Lord. Vision of Isaiah also distinguished between the Lord, who is the one who comes down to defeat Belial, and God, who is called the Most High, the God of Truth who sits in the upper world on High.
I can see Beloved and Christ being interchangeable. But in the core of Vision of Isaiah the name Jesus is not used. So in Vision of Isiah we have the Beloved Lord and God and in the Pauline letters we have Christ the Lord and God.
It seems possible that this is the first layer of the Pauline works. The name Jesus could have been introduced by Marcionite editors to tie the Pauline letters to a narrative in which the name Jesus was used.
Just considering the possibility.