"You're not Sherlock Holmes;
You're an editor!"
Mrs. Hope Stinson
'Too Close For Comfort'
Here's another example of Sherlock Holmes' existence in Earth Prime-Time as a character as real as Mrs. Stinson and Henry Rush (whom she was addressing.)
There was no mention of books or movies or TV shows. It would be just as if Mrs. Stinson was telling Henry he was no J. Edgar Hoover.
In that same episode, same scene, she said:
"Go to it, Agatha Christie!"
Dame Agatha Christie was a real person in the Trueniverse, but she also has several televersions, one of whom shared an adventure with the Doctor.
- 'Doctor Who' - "The Unicorn And The Wasp"
- 'Too Close For Comfort' - "Late, Great Herbert Maxwell"