sold at fair stalls, have had as many as 500 painting attributed to them. The avenues for research have been limited by many historical factors. Many archives were destroyed in bombing campaigns in the two world wars, and a great number of works for which records do exist are themselves lost or destroyed. The record-keeping in the region was inconsistent, and often the export of works by major artists was, owing to the pressures of commercial demand, not adequately recorded. The practice of signing and dating works was rare until the 1420s, and while the inventories of collectors may have elaborately described the works, they attached little importance to recording the artist or workshop that produced them. Surviving documentation tends to come from inventories, wills, payment accounts, employment contracts and guild records and regulations. Because Jan van Eyck's life is well documented in comparison to his contemporary painters, and because he was so clearly the period's innovator, a great number of works were attributed to him after art historians began to research the period. Today Jan is credited with about 26–28 extant works. This reduced number in part follows from the identification of other mid-15th-century painters such as van der Weyden, Christus and Memling, while Hubert, so highly regarded by late-19th-century critics, is now relegated as a secondary figure with no works definitively attributed to him. Many early Netherlandish masters have not been identified, and are today known by "names of convenience", usually of the "Master of ..." format. The practice lacks an established descriptor in English, but the "notname" term is often used, a derivative of a German term. Collecting a group of works under one notname is often contentious; a set of works assigned one notname could have been produced by various artists whose artistic similarities can be explained by shared geography, training, and response to market-demand influences. Some major artists who were known by pseudonyms are now identified, sometimes controversially, as in the case of Campin, who is usually, but not always, associated with the Master of Flémalle. Many unidentified late-14th- and early-15th-century northern artists were of the first rank, but have suffered academic neglect because they have not been attached to any historical person; as Nash puts it, "much of what cannot be firmly attributed remains less studied". Some art historians believe that this situation has fostered a lack of caution in connecting works with historical