possible data validation from multiple sheets

Hello, I have an excel doc with multiple tabs, that represent different era's in a game I play. Each sheet is exactly the same except for the amounts that it takes to level a great building (column C) of that era, and the rewards for each great building (columns V-Z) as it levels. I am trying to make a main page that can do data validation to both represent the sheet number (cell A8) (Which I cannot figure out), and the level of the great building (cell A18) (Currently A18 does change how the level of the rewards work, but not for every sheet combined, just each sheet individually works). I have been researching for hours, and it just seems I cant data validate over multiple sheets into 1 sheet, but maybe i'm doing it wrong or theres another function to use. I've looked into the INDIRECT function as well but cant seem to figure it out.


This is also my first post, and I dont know how to attach my file if that will help.