Did you receive a title, registration, or just a bill of sale from the previous owner?
I'm not sure about Colorado but in NY if I purchased a trailer that had not been registered since April of 2007 our DMV needs to know the following:
1) How much I paid for the trailer so they can charge me sales tax on the purchase price. (If the trailer is fairly new they may go by their book price and not what I paid) For example, Say I bought a 2006 trailer and paid $1000. Unless I have a receipt proving what I paid they could look it up and say its worth $2500 and charge sales tax on that price. It doesn't happen too much with trailers but I have seen it happen registering a car. (We have to pay sales tax on a vehicle each time it transfers ownership and is registered).
2) Our DMV usually goes by the previous title or registration as to how much the trailer weighs empty and how much the weight capacity is so they can charge us the proper registration fee. (the empty weight and max capacity are shown on our registration and registration fee is based on weight).
3) If registered for over 3000 lb it must have working brakes.
4) It must be inspected (so the state can collect another fee)
5) Make and year of the trailer and number of axles.
6) DMV shouldn't make you bring it up to date or make you pay back registration fees. Only from the time you register it.
Your DMV may vary as each state is different. Some don't require it to be registered. Some register by the year or every two or some I've seen are 7 years. Hopefully another member from your state will help fill you in.
