Q:

Date format for file's "Modified" and "Last opened" is different than other files

I have a few files in the same folder and I noticed that the format for the Modified and Last opened metadata fields are the "short" format for most files and the "medium" format for just a few. Why is this and how is this set for a given file?
Example of "short" format date:

Example of "medium" format date:

Just FYI, here's where the date formats are set in System Preferences:

A:

The date "presentation" of a file info in column view in the preview column is determined by the column width! The wider the column the more detailed the date!
You can easily check this by either alt-holding and moving the column handle which increases/decreases all columns at once or just moving the "preview" handle. The handles are the two small parallel lines near the bottom of a window.
very short (all examples are german date formats):

middle:

full:

