It’s possible Hoover knew what a low character Byrd was and just ignored him.
If only 750 pages of his FBI file have been released, we can well imagine what fun stuff was in Mr. Hoover’s private file. Byrd’s only real claim to fame was his ability to ear mark and suck up funds, including considerable funding for the FBI Automated Fingerprint Lab in WV.
I am unable to find one real important piece of legislation ever drafted by Byrd even though he was the longest serving Senator.