GDG - Absolute Generation and Version Numbers

An absolute generation and version number is used to identify a specific generation of a GDG. The generation and version numbers are in the form GxxxxVyy, where xxxx is an unsigned 4-digit decimal generation number (0001 through 9999) and yy is an unsigned 2-digit decimal version number (00 through 99). For example:
A.B.C.G0001V00 is generation data set 1, version 0, in generation data group A.B.C.
A.B.C.G0009V01 is generation data set 9, version 1, in generation data group A.B.C.
The number of generations and versions is limited by the number of digits in the absolute generation name; that is, there can be 9,999 generations. Each generation can have 100 versions. The system automatically maintains the generation number. The number of generations kept depends on the size of the generation index. For example, if the size of the generation index permits ten entries, the ten latest generations can be maintained in the GDG.
The version number lets you perform normal data set operations without disrupting the management of the GDG. For example, if you want to update the second generation in a 3-generation group, replace generation 2, version 0, with generation 2, version 1. Only one version is kept for each generation.
You can catalog a generation using either absolute or relative numbers. When a generation is cataloged, a generation and version number is placed as a low-level entry in the GDG. To catalog a version number other than V00, you must use an absolute generation and version number.
You can catalog a new version of a specific generation automatically by specifying the old generation number along with a new version number. For example, if generation A.B.C.G0005V00 is cataloged and you now create and catalog A.B.C.G0005V01, the new entry is cataloged in the location previously occupied by A.B.C.G0005V00. The old entry is removed from the catalog, to make room for the newer version, and may or may not be scratched depending on what limit processing options are specified for the GDG base. For system-managed data sets, if scratch is specified, the older version is scratched from the volume. If noscratch is specified, or if the attempt to scratch the DSCB fails, the older version is not scratched and the generation data sets is recataloged as a non-VSAM data set with the GnnnnVnn name not associated with the GDG base. For non-system-managed data sets, the older version is also governed by the GDG base limit processing options. If noscratch is specified for the base, the older GDS version is not scratched. To scratch the old version and make its space available for reallocation, include a DD statement, describing the data set to be deleted, with DISP=(OLD,DELETE) when the data set is to be replaced by the new version.