Ah, you're right (W20 != 20). The basement wiring closet was Building 16, but the SIPB stuff was W20. (you can tell by the ghetto furniture with duct tape).
SIPB at least used to be pretty friendly about letting visiting "reasonable" people plug into the network, based on whoever was at the office at the time.
I assume this is a typo? or is there a recent renumbered bldg?