Large companies like IBM, Microsoft, or Novell typically had a well defined process for releasing software on floppies. More often than not, files were not directly copied onto a physical floppy; instead, a tool was used to create an image of a floppy disk from distribution files, and the image was then sent off for mass duplication.
Quite often, timestamps of files were set to a predefined value when creating the image. That practice is probably as old as timestamps in the FAT file system. PC DOS 1.0 kept track of the date when a file was modified, but not the time of day. PC DOS 1.0 has all non-system files set to a 08/04/1981 date, although it is theoretically possible that this was a result of normal file manipulation.
With PC DOS 1.1, there is no ambiguity. The timestamps of all files are set to 12:00:00 on 05/07/1982. Floppy disks are not nearly fast enough to write all those files within two seconds (the FAT timestamp resolution), even in the extremely unlikely case that someone sat there waiting until exactly noon to start the operation. It is a given that IBM artificially set the timestamps of all files to match, and that was before the PC was even a year old.
It is notable that Novell followed a different strategy and strictly kept the original timestamps of shipping files. It was common that different releases had some files with matching timestamps and some files different. One could be reasonably confident that two files with the same name and timestamp were in fact identical. That was not always the case with IBM or Microsoft, where two files with different timestamps were often identical. And in rare cases, two different versions of a file were distributed with the same timestamp, arguably completely defeating the purpose of timestamps.
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