So they're still using random date formats for each new folder, years after the initial mess was cleaned up? Could the problem be fixed at the source? Or are the folder names outside anyone's control, and not all being made by the same people or organisation?
You'll never get a script or regex that can handle every possible date format because they're going to clash with each other and have ambiguities (unless they use month names and separators between components, but they aren't using those it seems).
If the folders have the right dates in their Modified or Created timestamps, you can use those to set the folder names without having to try to parse the existing names.