Service Dog Notice after Lease Ended

[Stacy Ngo]

Seeking some help because I am unsure as to what to do at this point. 

My tenant's lease has been over for a month now. We have been talking lately about their move out inspection damages. As of today, they mentioned that they were not aware of the law in Colorado that you didn't have to pay pet rent or a pet fee for a service dog, which they have. During their whole 2 years, they paid pet rent and a pet fee. Of course, we were never aware that their dog was a service dog, nor did they ever tell us or send in the registration forms. 

Is this something to be worried about at this point even though the lease is over? 

Is this something I should seek legal advice for or am I being too paranoid?