A method of enabling subsequent validation of an item having a data tag. Data may be read from a tag using an electronic reader. A readable marker, such as a barcode, may be selected from a plurality of different readable markers and applied in proximity to the tag. An association request can be created and communicated to a database, where the association request comprises data from the tag and data relating to the selected readable marker, so that the database may use data from the association request for subsequent validation of the tag. An authentication database for recording an association between a data tag and a readable marker applied to an item carrying that data tag are also described.