Make a list of exact match duplicates in large spreadsheet

I attached my original results when I tried this yesterday. I came to this by clicking conditional formatting --> Highlight cell rules --> Duplicate Values. Then I sorted column A by cell color (light red) to be on top, then by column A value. When you look you will see some values do not have a duplicate, I'm confused as to why this is.

I would really like all of the duplicates grouped together in the same column as the other part numbers. kind of like it's shown in the attached file.