I wouldn't worry too much about it.
You might never get the papers you wanted.
Possession is 9/10 of the law, if original breeder hasn't worried about getting their money by now, I doubt they will be too eager to come after you now.
I would just sit tight and let the breeder make the first move. Why spend a bunch of $$$ on a lawyer if it isn't necessary.
But do keep track of all bills paid on the horse and anything that proves you are the owner of the horse. I hope you got a bill of sale.
The best time to plant a tree was 20 years ago, the second best time is today.