Run Sales Reports from Multiple Sheets within a ever expanding workbook

Hello, I would still consider myself a newbie when it comes to utilizing the potential excel has to offer. With that being said, I need to extract data to run sales reports from multiple tabs within a workbook. Every tab is labeled a month of the year.
Within each tab there are 8 columns which remain the same. The rows are actually repeat and newly captured clients and very by number each month. I need to figure out a way to be able to continually add new months (tabs) of sales data while continually being able to run the reports. I really would like to utilize the pivot tables if possible. Can anyone assist me in how to merge the data? Thank you!

I want to run a report to find out how much commission was paid our per client. Some clients will appear in multiple months (tabs/worksheets). I would also like to know how much commission has been paid with each company. These are only two examples of what I would like to do with this spreadsheet. I continually add months as they close so the formula or calculation must account for adding new months (tabs/worksheets). I would like to be able to specify which months I choose to include in my reports based on quarterly, same month but different year, one full calendar year, etc.

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Thank you Mysore your code worked!