@thestumbler A similar question was asked a week ago in this thread, please read it for details.
I personally believe that it would be extremely rare being able to use the same schematic for both through hole and smt versions of the board. That means that all your pth components would need to have not just the same number of pins but also the same pin numbering as your smt components. One single difference between the two would ruin the concept.
But if you have other use cases then you can absolutely use the same sheet in more than one schematic (even though it’s not located in the project directory).