on a tester's pc (no dev tools) creating a zip had several messages along lines of
"this folder already contains a file named 'Test\ABCDEF~1.XYZ'"
If I look thru explorer then I can see for above example there are files called
ABCDEF~1.XYZ
ABCDEFG.XYZ
ABCDEFGHIJKL.XYZ
If I look thru DIR /X in Cmd
it shows the only one with a shortname is
ABCDEF~2.XYZ ABCDEFGHIJKL.XYZ