Directory search in Windows Command Prompt shows incorrect output

dir /x

For compatibility reasons, Windows generates a 8.3 name for every long file name created, and wildcard matching code (FindFirstFile()) checks both the original and shortened names. Use dir /x to see what short names are assigned to each file.

Usually the auto-generated short names look like 090820~1.PDF and 090820~2.PDF and so on, but there are exceptions:

[...] if at least 4 files or folders already exist with the same initial 6 characters in their short names, the stripped LFN is instead truncated to the first 2 letters of the basename (or 1 if the basename has only 1 letter), followed by 4 hexadecimal digits derived from an undocumented hash of the filename, followed [...]

Moving a file within the same partition does not change either of its names, only relocates them.

When using the NTFS filesystem, 8.3 name creation can be disabled system-wide using:

fsutil behavior set disable8dot3

However, this won't affect existing names.