In Texas we have to have a "Certificate of Number for a Vessel" card on the boat, and present it to the Game Warden if he checks us at the lake. The card doesn't say anything about the motor on the boat, but I'm fairly certain you only get one of the cards if you have proof of titles for both the boat and motor when you go in to register the boat.
I had a ridiculous issue that I had to resolve when I was trying to register my boat. The guy I bought it from gave me the titles from the original owner. He had never registered it in his name. I spent about 6 months rebuilding the boat, and went to get it registered when it was ready to go to the lake. By this time, the guy I bought it from had moved out of state, to Louisiana. When I ran into trouble at the TPWD office, I called him to tell him the problem, and he told me it was my problem. So, I went on a search for the original owner, only to find out that he had passed away 10 years ago. So, I explained all this to the folks at the TPWD office, and they gave me several forms to fill out. The important one, was a Request to skip Titling by Previous owner or something similar. The form gave me the ability to explain in paragraphs what my situation was. This form, along with several of the other forms were then faxed up to the TPWD headquarters for approval. A few hours later, they approved everything, and faxed it back. It was a lot of work to get it all done, but I'm glad I'm fully legal and have nothing to worry about if a Game Warden happens to stop me.