The ‘common knowledge’ defence is a legal strategy which has been successfully used by defendant tobacco companies to avoid legal responsibility for the harms caused by smoking. Tobacco companies have hired professional historians to try to persuade courts about a longstanding high level of public awareness regarding the risks of tobacco use. To support this argument, they have used archival news clippings and media reports. Two historians were hired by tobacco companies to offer this defence during a recent class action trial in Canada, following which they were required to submit to the court the collection of media materials which had been gathered by history students to assist their testimony. Included in this collection were tobacco advertisements and other news items about tobacco products which the students had inadvertently also collected. Quantifying this collection reveals that even by the tobacco industry's own construct, the information environment surrounding Quebec smokers in the middle 20th century included more prosmoking messages than information about the risks of smoking.