I know that generally, old claims need to still be notable today to be allowable here. This makes a whole lot of sense in that it isn't worth debunking obsolete scientific theories that haven't been believed by anyone worth mentioning in ages (e.g. the luminiferous ether or the four humours theory of disease).
I recently encountered a different sort of "old" claim. I found a newspaper column from the early 20th century warning readers that a certain manufacturer of cigarettes operating in the newspaper's city was lacing their products with opium and thus their smokes should be avoided by smart consumers, but without specifying how this product adulteration was discovered (e.g. laboratory analysis by a specific cited scientist).
So many changes have been made to both the manufacturing and regulatory side of tobacco products in the past hundred years that asking people today if they believe that cigarettes laced with opium are made in the city today is pretty much meaningless with respect to the original claim.
The claim to be analyzed, then, would be whether such adulterated cigarettes were manufactured and sold then and not whether they are being manufactured and sold today. Is it, then, sufficient to show that the claim was believed by people then, or do I still have to show that this historical claim (opium-laced cigarettes were manufactured and sold by Company X in City Y in 191x) is accepted today as a historical fact by a significant number of people?