Hi Jeff,
This is what I meant by reference table.
Also, as you want it to be Numeric, can you update the filter definition as below and check what happens? Notice, I changed it back to 'N'. It worked for me.
1 = @Prompt('Enter Fiscal Year Period (e.g. 1 for July):','N',{'1','2','3','4','5','6','7','8','9','10','11','12'},Mono,,Persistent,,User:0)
Thanks,
Mahboob Mohammed