If neither the MD field nor the CN field exists, a value of 0 is entered as the UD code. The MSDS database contains the most recent MSDSs available from suppliers.
Most suppliers update their collections in the database monthly or quarterly.
MSDSs may be several years old and still be valid. When the UD field contains 0, it simply means that the reference fields of the MSDS do not contain a relevant date. Some of the MSDSs may contain a date in the text of the document which has not been extracted to any reference field. Searches can be narrowed down by using this field. Browsing the index will reveal that the majority of the MSDSs have update codes within 2 years of the production date of the database.