Continuing the discussion from License?:
Has anyone ever known this to actually happen without an incident or a report? I know a case where a mate with a near coastal license and no towing endorsement did a few tug deliveries 10 years ago and I highly doubt anyone ever looked into that.
If he was just doing deliveries, would he need towing endorsement?
Any operation of a towing vessel requires a towing license, even light boat deliveries.
Do you have a reference for this? Because I also may know a guy who delivered some light boat tugs without a towing endorsement 
46 CFR 15.535. There are no exceptions for light boat, deliveries, harbor assist, etc. If it’s a towing vessel, it applies. Getting away with something doesn’t necessarily mean it’s allowed. See also “FAQ” no. 19 in Enclosure (1) to NVIC 03-16.
I was hired once as master of towing vessels to deliver a light tug. The USCG had been on board and would not allow the owner to move the boat. He had a 200 NC license.