Question : Multiple Asset tracking per month / Per year

OK, I have having a melt down over this problem.  I cannot seem to get started in the right direction.  I have Excel data that needs to be in an Access form/datasheet format.  Currently an employee enters sales data at the end of the month for child tenants to the parent Center.  Now, there are many Centers, each center has many tenants, each tenant has sales data, sales data is recorded every month of every year.  Granted some years a center may have the same tenants, more tenants or less tenants.  So the way this data is being recorded now is by adding a tab in Excel for the year, coping /pasting the layout to the new page, deleting the sales data and away we go for the New Year.  What they want is to be able to have all this data in a central location and not a bunch of different Excel docs.  I cannot seem to figure out how to have several years AND several months for several tenants.  Please help.
I attatched an example of what a current Excel file looks like.

Answer : Multiple Asset tracking per month / Per year

You could even design the Access form similar way as it is done in Excel - means separate page tab for each year but it would slow down the form from certain number of tabs. To design a combo with the year selection should be sufficient.