in the server validation behavior, set the failed redirect to the form page and pass a URL variable:
update.php?valid=false
you can create a ternary expression to use the validated entries value if the URL variable valid is equal to false, or use the recordset value if not, for example:
<?php echo(((isset($_GET['valid']) && $_GET['valid'] = "false"))?ValidatedField("update","firstName"):$row_recordsetName['FirstName']) ?>

