Folks from CO should probably comment, but here in CA you would want to check the VIN in DMV records. If a vehicle license has expired, it accrues back fees, and after just a few years the fees owed can exceed the value. You will want to research that WRT CO, and also how fees owed CO affects registration in your home state.
Edit: I now see you are also a CO resident, so reciprocity is not an issue here.
I just bought a motorhome that had never been registered or had the title transferred by the guy I bought it from. The title was clear but did not reflect the transfer of ownership to the guy I bought it from. The title was signed by the previous owner who sold it to the guy I bought it from(short term flipper).
The DMV didn't care about the previous owners registration status in Arizona. They accepted the title as is since it was signed by the last recorded owner. I have to register it myself as soon as it's running but I'm not responsible for the previous owners paperwork. Different states treat registration differently though so YMMV. Don't sweat it going into the DMV. They see stuff like this all the time especially with trailers and MH.
Long ago, here in Montana, when planning to sell a anything that had a title, we could go get the title notarized without filling in the buyer's name. We then had an "open title", that any body could fill in the blank, transfer the title, and own the vehicle. It was great in a way, because if somebody came to buy it, we could just hand them the title.
Now, however, it is against the law to have an "open title". In fact, the notary will not sign the title unless the buyer's name and address is filled in.
Anyway, if the CO title for the trailer is an "open title", in that the previous owners signed it but the buyers names are not entered, no problem, just put your name in the proper blanks and go register it. If the buyer's names are filled in, they might allow you to register it based on a Bill Of Sale from them. But, check with the CO DMV or MVD BEFORE you give them any money!
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