System and user labels within a tape or a file must always appear in a specific order. Tape marks are not permitted within label groups. Each label group must be located completely on the tape containing the first label of this group.
Each label group begins with the label with the number 1 (HDR1, EOF1, EOV1, UVL1), except for UHL (UHL0) and UTL (UTL0). This first label is followed by all other labels of the same group; these must be arranged in ascending order of the label numbers, with no gaps in the sequence.
The number of end-of-file and end-of-volume labels (EOF/EOV) must be equal to the number of file header labels (HDR).
If a tape or a file (or a volume or file set) contains both system labels and user labels, each user label group follows the appropriate system label group.
In the case of user labels, the number of user trailer labels (UTL) is not determined by the number of user file header labels (UHL).