I don't know if this is really possible with just functions, but I want to avoid macros and code behind the Excel to accomplish this.
Let's say I have a Workbook that has X amount of sheets, with the first sheet being a cover sheet. Each additional sheet in the Workbook will be a set of data named something specific ("Car", "Desk", "Chair", "House").
On the cover sheet, I would have a selection list of all of the sheet names, an 'input' cell for a particular number, a 'date' cell for a date in the past, and a final 'output' cell at the end. The idea would be to allow someone to enter a number in the input cell, a date in the date cell, and select a sheet name from the selection list. The formula should, then, be smart enough to find that sheet based on the selection list, then use the date to search through the data set (based on year and month for the row and column respectively) and final use the found cell to plug in to the final formula and display a calculated 'output' for the output cell.
I'm sure I can figure out the searching by date in a data set and doing the formula, but I have no clue where to start with trying to dynamically target a sheet to look through.