Do pets really know their own names?

I'm honestly not sure about my cats and they are 13 and 14. But, I know our dog knows his name. We got him in May at 13 months. He was with a family for 10 months and a shelter for 3 months. The family called him Cujo. The shelter called him Miles. We named him Dorian. We thought we'd see what he'd answer to just a few weeks ago. He will still answer to the name Cujo. He looks at us like we're stupid if we call him Miles, but he will run happily to us when we call him Dorian. We won't ever call him Cujo again. He was abused by his former owners and he cowers when we use that name. It's really sad.