A Clarification
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For OS/360, OS/VS (VS1, SVS and MVS), IBM never shipped much (if any) source code with the "distribution materials" (PID tapes).
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Customers had to order the "optional source materials" for each new version/elease,? and for each major component.? Those optional source tapes were always one release behind the current version, so assembling that source produced object code that never matched what was currently shipped, unless that module just had no maintenance (PTFs) applied (highly unlikely) in the interim.
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So, the source code we have for "MVS 3.8j" is actually MVS 3.7 level code.
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Hence, the hours of work needed by Paul Gorlinsky and others to recreate a version of source code that matches the current version of the object code.
