It appears that plaques such as these were usually attached to imperial seals which were visible evidence of the emperor's authority and legitimacy, ratifying every edict, decree and appointment. Qianlong reformed the use of such seals and in 1746 restricted their number to 25. For examples of comparable ivory labels still attached to a seal, see, The Complete Collection of Treasures of the Palace Museum, Jadeware (III), p. 2, fig. 2 and The Forbidden City, Rotterdam, 1990, p. 222, fig. 74 and p. 225, fig. 76. See also Exhibition Palast-museum Peking. Schatze aus der Verbotenen Stadt, Berlin, 1985, Catalogue nos. 1 and 12.
Another example is illustrated in Transactions of the Oriental Ceramic Society, 1963-64, included in the exhibition, 'Arts of the Ch'ing Dynasty', cat. no. 88, another, attached to a seal, is illustrated in The Forbidden City, Rotterdam, 1990, cat. no. 76.
Compare also, the example sold in our Hong Kong Rooms, 29 April 2002, lot 588