"Anna, help me do battle with this monstrosity.
It looks like a creature from the lost world."
Lady Violet Crawley
The Dowager Countess was referring to a hideous floral bouquet chosen by Lady Cora to decorate one of the rooms in the mansion, but it was still stated in such a way as to suggest that the reference was to the actual location and not to the work of fiction by Sir Arthur Conan Doyle.
There have been a few TV portrayals of Professor George Challenger, protagonist of the novel (and member of the Wold Newton family). But as it was the first to involve a TV series, I give the main Toobworld position to the Challenger played by Peter McCauley. (Although I preferred Bob Hoskns or John Rhys-Davies; Claude Rains from the Cineverse for that matter.)
The televersion of 'The Lost World' ended on a cliff-hanger at the end of Season Three, but plans for two more seasons were revealed by the producers of an eventual return to the civilized world by most of the adventurers - only to the year 2005. I think Challenger at least would have been returned to his original timeline, and back in London. (To have returned them all might have been too much of a disruption for the flow of History.) And in order for Lady Violet to have made that cutting remark about the cuttings, Challenger had to have returned before November of 1916.
Unlike the Society of 2005, the earlier incarnation of the London Zoological Society debunked Challenger's claims (once he returned.) This would be why his return to that timeline (by the Doctor?) did not disrupt the established events. But eventually there was no hiding the truth that he had found a plateau in South America which was the land that Time forgot.
And I would not be surprised if Lady Violet had been one of the financial backers of that expedition, which is why she was conversant with that lost world......