This value can't be used for checks because the real exit code of the process might just match.
So I believe this field should either be omitted for a running process altogether, or be set to a value outside of the valid retvals range.
259 is well known value STILL_ACTIVE, returned by GetExitCodeProcess|Thread. Applications should avoid to return it.
I consider it's admissible. But of course, you should to check Status to be sure.
This value can't be used for checks because the real exit code of the process might just match. So I believe this field should either be omitted for a running process altogether, or be set to a value outside of the valid retvals range.