First, informix doesn't require the "date" internal function like other databases. If informix can't do a legal conversion it does it. Also, your syntax is off somewhat:
WHERE ESC.discov_date between "9/18/03" AND "9/19/03"
The above 2-digit year works only if shell variable DBDATE equals MDY2/
The default for DBDATE is MDY4/ and if it's set this way it's:
WHERE ESC.discov_date between "9/18/2003" AND "9/19/2003"
Regards,
Ed