But officially they are two series, sharing a sequence. Series may have multiple organizations. But wait, there is more. A report may come out under multiple series. The series may share the entire document, or have distinct covers and share only the body.
Bibliographic information includes a mix of acknowledged information and artifact description.
So while it often describes a version, the body may drift out of sync, affecting fields like page count. PostScript One has the PostScript file of a report. Sometimes you have two PostScript files, as when the report is long or multiple generators were used. Some meta information is specific, and some is shared. Sometimes you have two PostScript files, and the are subtly different versions of the same report.