Hello my good friend StanJ. I take it you don't believe that Moses spoke with Jesus face to face before His incarnation. Moses certainly new the name of the Messiah because he gave that name to Hoshea the son of Nun, whom we commonly know as Joshua. (Joshua is a "type" of the Lord.)
These are the names of the men whom Moses sent to spy out the land. And Moses called Hoshea the son of Nun, Joshua. Numbers 13:16
Do you think that Agur, the son of Jakeh, was referring to "Logas" as the name of God? Who has ascended into heaven, or descended? Who has gathered the wind in His fists? Who has bound the waters in a garment? Who has established all the ends of the earth? What is His name, and what is His Son's name, if you know? Proverbs 30:4
Since Logas is a Greek word and concept, what would be the Hebrew equivalent?
What do you base your assertion upon with regard to Hebrews 13:8, other than the metaphorical passage in the 1st chapter of John's gospel?