I’m not quite sure what it is that you are doing, though. Both sheet number and sheet name are built-in ‘text field properties’ and it shouldn’t be necessary for you to define these yourself in custom Document User Text key-value pairs. (And scale is on the wish list as RH-12602 and RH-31361).
Could you provide a 3dm file that shows what you are trying to accomplish?
BTW, I’m trying to keep an overview of text field workflows in the following thread: