I just got of the phone with NJ DMV and they told me that I have to display both – NJ registration numbers (plus decals) on the outside of the boat and USCG numbers inside of the boat. They also told me that in NJ I need both, title and certificate of documentation (if the boat is documented). I guess NJ is different.
I'm not sure you got the correct info. All of the above is true EXCEPT you DO NOT need to display the state registration numbers on your hull, JUST the N.J. stickers. You must affix your documentation number permanently to your hull as per the U.S. Coast Guard. I live in N.J. and just completed the documentation process directly with the Coast Guard. Very easy to do. I urge you to call the Coast Guard directly...they are very friendly and quite helpful! You can get the toll free number from their documentation website.