There currently isn't an option of "Year, Year & Month, and None" in Pivot when assigning rows, using the system column "created date" in Smartsheet.
To create a Dashboard it is very useful to have that option. At the moment i need to workaround with some extra colums to convert the date first into a Pivot readable format. Or using a Automated Date Column to create a readable date format, this is only useful for new smartsheets.