Case of the careless credit union

[needhlp66]

What is the name of your state? CA
I was divorced 4 years ago. Part of the settlement was that we would separate his cr. cards and my cr. cards. In addition, he was to refi his car and 1/2 of a signature loan and I was to do the same for my car and 1/2 of the loan. I did as agreed and have since paid for my car & loan. He didn't, however, and they repo'd his car 3 years ago and never pursued collection of his share from him for either debt. The credit union, in a board meeting, agreed to separate our debts. They established separate accounts for both of us and when they repo'd his car they only wrote it off under his name.
The same financial institution did not pursue me for any amount of his debt either-when I think legally they could've at that time. A few months ago I paid my car off and they're holding my pink slip "hostage" saying that they lost money on his car so I can't get my pink slip until they recover the money from his debt. Is it legal for them to pursue collection 3 years later after never contacting me about the loss or giving me a chance to pay the debt? They conveniently cannot find record of them repossessing his car or what amount they collected for the car in auction. They are in the process with the DMV to find out who owns the car now.
In addition, they approved me for a 2nd car loan just after they wrote off his loan (w/in 2 mos) and they have never reported any derogatory info to my credit bureau. Furthermore, they've allowed me to borrow against my signature loan several times over the years and never mentioned this. My monthly statements never indicate another balance owed. I also purchased a house and they submitted letters that my account had been in good standing with them (that was 1 1/2 yrs ago).
I am aware that a 3rd party doesn't have to honor a sep of debt, but isn't there some kind of time frame for how long they can wait to decide to collect on a debt? Can someone let me know if I am just stuck and out of a car or is this illegal?What is the name of your state?