To close the loop on this, Verizon Wireless reported to me that they fixed the issue (whatever it was).

They further said that 63.56.37.4 was a typo; all IPs should have been in 63.59.x.x.

I am able to reach the 63.59.0.0/16 IPs in question: 63.59.39.232 & 63.59.67.68.

Justin: Thanks for the detail that this was reproducible from Cogent's looking glass. I think there's a good chance that contributed to them being able to find it (i.e. having an easy way for them to test).

-- 
Richard