Sheena,

>problem with sytax, this statement isn't working, are my brackets in wrong spot?
>
>replace all May_1998 with 2 for May_1998 = 0 and ((start_da < {1998/06/01}) and (final_da > {1998/05/01}))

Use the unambiguous file format by adding ^ after the first bracket:

{^1998/06/01}