An efficient supply chain relies on identifiers. Ideally they are industry identifiers. However, while industry identifiers such as ISRC, ISWC, UPC etc are becoming more and more common, there are still plenty of proprietary identifiers in use today.
The use of proprietary identifier is discouraged for all messages (with one crucial exception, for sales reports where all available identifiers should be communicated to aid matching algorithms) if an industry identifier has been allocated. Thus the following snippet from a Release delivery message should not be used:
Instead just the ISRC should be provided:
Of course, should no industry identifier be available, the use of proprietary identifiers is encouraged.