You'll probably need Narkissos to tell you the technical details, but my very remote knowledge of Heb leads me to conclude that this expression may indeed have biblical sanction, since it occurs in the early chapters of Genesis.
Gen 2:4,5,7,8,15, 16, 18,21,22,; 3:8,8,9,13,14,21,22,23, use the expression YHWH ELOHIM which NWT has as "Jehovah God" and which the JB renders as "Yahweh God"
To the best of my knowledge this expression does not occur outside Gen chaps 2, and 3, but then I do not have a Heb language concordance.
I am not sure of the significance of this expression, but the OT Bible Knowledge Commentary says on pg 30: "The repeated emphasis on [Yahweh] God is significant. The sovereign creator of Chap 1 is also the covenant-making Yahweh of Israel.Thus Israel would know that her Yahweh had created everything and that it was He who had formed mankind by special design"
The Inter-Varsity Press Bible Commentary has a fuller note: "The combination of the generic "Elohim" and the proper name Yahweh, is found repeatedly in Gen 2 and 3. "Elohim" is used in Gen 1 for God as creator, and it denotes God as He is known through His revelation in creation, and general providence,including man's inward and intuitive knowledge of God. "Yahweh" is used alone beginning with Gen 4. It is God's personal name describing Him as revealed through His historical-covenental revelation as the Lord of eschatalogical purpose and soverign fulfillment.This transitional combination, "Yahweh God" in Gen 2 and 3 serves to identify Yahweh, the covenant Lord, as God the creator.Such multiple designations of Deity were common in the biblical world" [pg 83]
Cheers