I don't think anyone has mentioned that of course the gospels were not written till late in the 1st Cent. (Mark may have been as early as say 60CE, but a number of scholars feel it is later)
So, in the decades after Jesus death the Good News of the Kingdom must have come from the O.T, any witness about Jesus must have been oral.
So, a question comes to mind , the WT claims to be preaching what the Apostles and disciples taught in the 1st. Cent., so why do they not eschew using the N.T and just stick to the Hebrew Scriptures as their Ist. Cent. pioneers did?