When identifying books, the EAN/UCC-13 or UCC-12 should be attempted prior to choosing ISBN, ISMN, or ISSN.
The EAN.UCC Prefix 978 is always added in fron of the ISBN number.
The EAN.UCC Prefix 979 is always added in fron of the ISMN number.
The EAN.UCC Prefix 977 is always added in fron of the ISSN number.
Two-digit Add-On Symbol
Serial publications can use a 2-digit symbol to help identify its nature of being Dailies, Weeklies, Bi-Weeklies, Monthlies, Quarteries, Annuals or Special intervals.
The two-digit symbol is placed to the right of the original GTIN symbol and parallel to it. And the same print quality apply.