Well, enough research to be sure you’ve done the paperwork correctly and so actually own the thing for starters! Is there nothing on the actual form that indicated the deadline or at least refers you elsewhere to find out the requirements?
Presumably there was no paperwork to be done on your purchase of your ring beyond handing over money and getting a receipt in return - so not much if anything to check.
I’d wager that you did at least some research before you bought your ring? That you at least made sure that you were not about to become the proud owner of a piece of glass encased in chicken wire for which you got snookered into paying thousands of dollars, but instead something a little more genuinely rare and precious and subsequently more worth what was paid for it? That you perhaps insured it and had it valued, as most people do with valuable jewellery?
You bought a car, not a piece of jewellery. You already know that there is much more paperwork involved - in that sense it is more like buying a house than your ring. Simple rule - the more paperwork, the more hidden catches and things that can go wrong. The more checking, therefore, required to ensure that nothing comes back to bite you.
Heck, I’ve never even bought a car personally and yet still I know, mostly because I know people who have bought em, that it’s not just a simple matter of hand over money and drive away. I’ve also seen, when in my local Transport office to get my licence, that they put out booklets about buying and selling cars - which I’m sure would outline the sorts of rule that tripped you up.
Prudence dictates that I would give such a booklet a glance prior to purchasing a vehicle, as I would the guides put out by my state’s Real Estate Institite about buying a house before I did so.
Never seen the equivalent in a jewellery shop or a white goods store