>Yes, you're right. I shouldn't be using sys(3), but I'll use SUBSTR(SYS(2015),3) as Tore suggests. SYS(2015) returns a string starting with an underscore followed by a number, which is why you need to start with the third character, which is a letter.

A file name can start with a digit and 3rd character in the string returned by SYS(2015) may be a digit also.