They probably let you return your set of hearing aids after 10 months because you bought a different brand from them. I wonder if you simply wanted to return for a refund 4 months after the trial period, whether they’d let you or not?
My brother tried to return his KS8 set to Costco only a week after the 6 month trial expired and they wouldn’t let him.
But you’re right, it doesn’t hurt to ask.