Hello, all experts.

I got a very troublesome problem. I have a table as below,
table a
col1 serial,
col2 date
DBDATE=DMY4
select * from a;
1210: Date could not be converted to month/day/year format
Seems there are some records has invalid date in "col2".
col1 col2
1 01/10/2003
2 01/10/2003
3 ??
4 01/10/2003
5 03/10/2003
6 01/11/2003
7 ??
8 ??
9 ??
...
...
1000 ??
1001 ??
...

I want to update these error records with a valid date at the same time remaining the correct records,
update a set col2='10/10/2002' where col2<'01/01/1900'
but I still got this error,
1210: Date could not be converted to month/day/year format
how can I do?
In addition, why are these corrupt data populated? I never inserted any invalid date into the table, actually I think even I want to insert an invalid date, it will be rejected by informix, right?

I will be very appreciated if anyone can give me a hand. Thanks in advance