It is standard practice in the Toobworld Dynamic that if a fictional character or place from another source is mentioned in a TV show, with no reference to the original source, then we can take the liverty of claiming it exists in Toobworld, even if there never was a TV adaptation for it.
'Downton Abbey' has been a source for several of these. One of them is that there were two references to pirates made famous in 'Treasure Island' written by Robert Louis Stephenson. Back in 1912, Thomas Barrow, the first footman, called Lord Grantham's new valet John Bates "Long John Silver" because of his bad leg and use of a cane.
A few years later Isobel Crawley's cook Mrs. Bird called Mrs. Pattmore (the cook of Downton Abbey) "Blind Pew".
In our world, "Treasure Island" is a work of fiction. But in Toobworld, it's an historical account. Actor Robert Newton is the official portrayal of Long John Silver in Earth Prime-Time. All of the other televersions of the one-legged plunderer occupy other TV dimensions.
As for Blind Pew, his character was killed off before the start of the TV series 'Long John Silver'.