I don't think any of us doubted the veracity of Mum's memories. We just thought that they were secondary memories, like yours about the excitement you felt in getting separate rooms.
We have an aunt who turned 103 on January 3rd. Physically frail, she recognizes people instantly, even those she hasn't seen for months, and can discuss their families quite coherently.
She is a source of comfort to me. On her example, I can expect another thirty-one years of productive writing.