The link you have specified is for uploading data into data tables using a spreadsheet. The requirement you are specifically looking for will just not work with uploading excel files into pega.
A case can have n number of fields, it is not advisable to store data in n number of columns in db as it causes performance issues. As you need to create cases, you need to also ensure that you skip already executed stages and steps and the case lands at the correct stage.
You may check the pega marketplace to see if there any tools that may help with this requirement