Ownership with no paperwork. Did that a few times, never again if I can help it. I have titles on all my junk.
My case was a boat. Dealing with the marine theft division was probably easier then dealing with the DMV. In my case I was dealing with 1 person the whole time. Took months, certified letters, and a prior owner sending back the letter stating they release all ownership of said vessel. As the officer who was doing the paperwork stated, it is easy if it is stolen. But if you can't find any record, there is another database you need to search, and another, and another. At some point you either find the paperwork, or you give up. And they don't want to give up without searching every possible option.
The other one I knew was clean, but still no paperwork. Have an old F150 truck bed trailer. Made in Kansas in the 90s, no title needed. Zero paperwork, the title was in the glove box when it was scrapped. Finally decided to get a legal AZ title on it. Down to the MVD and in a minute was diverted to a level two inspection. They wanted to hoist it and look for an old VIN on the frame. Humorous part was he was worried about my ability to back the trailer. I pointed to the VIN on top of the exposed frame rail and asked if that was what he wanted. He looked shocked. That one I had an assigned state VIN sticker inside of 15 minutes. Have a title and legal plates for that now as well.
Also had my fathers old homemade trailer with an AZ assigned VIN plate. He HAD a title for it from the 60s. Again in Kansas no registration on little trailers. I got it and simply filled an affidavit to the lost paperwork and they kept the old VIN plate.
I've had good luck so long as it comes up clean. And the stuff I got (except the boat) I knew had a clean history. Just took time. The boat we just got lucky with. Could have been in jail real fast with that one. But got the proper paperwork and at that point it could be used and later sold for a profit.