There are, however, good reasons for proceeding on the basis of secondary documents rather than on catalogue information derived from examination of materials. The people who should most welcome this information are in fact cataloguers themselves, since it enables them to assess where the copies they are examining are likely to belong in the historical tree relating to that particular work. It is also useful in tracing the history of the many, many films which are either lost or survive in places other than archival collections. Most countries have a system of statutory deposit for books and other published print materials, and the national libraries where these materials are deposited catalogue them with varying degrees of thoroughness. But in the case of films, very few European countries operate any equivalent system.
Films enter and leave circulation without ever passing into the hands of a qualified archivist.
Even films which do end up in archives often do so at the end of their commercial life, in versions which may be seriously downgraded compared with that in which they originally circulated. And the archives themselves, when they do get hold of the film, often do not have the staff to catalogue it properly. It is therefore a sheer practical necessity to rely on information like censorship records which may be the only place where one will find useful information like the length of a film at the time it was released to the public. So while I agree with Harriet Harrison that there are scientific reasons for preferring to rely on information compiled as a result of cataloguing of archival materials, I would also argue that for knowledge to progress it is sometimes necessary to play a game of leapfrog and supply information not derived from cataloguing practices, in the belief that this information in turn will help the cataloguers in their own scientific work. Finally a word on identification.