SQL & PL/SQL

I have some legacy data where one of the fields is a five digit number representing a date in 'rrddd' format. I need a query with a date condition on this column.

Simply put, I need a query like this:

select * from table
where to_date(lpad(status_date, 5, '0'), 'rrddd') >= sysdate - 10;

However, there's bad source data (of course there is!) which raises an ORA-1848 date conversion error.

So, I wrote a function to validate the dates first and embedded it into a subquery:

select v.* from
(select * from table
where is_valid_rrddd_date(status_date) = 'Y') v
where to_date(lpad(v.status_date, 5, '0'), 'rrddd') >= sysdate - 10;

The problem is the query is not sufficiently complex that the optimizer doesn't just roll-up the subquery and evaluate both conditions at the same time (or so I theorize), and it still raises the 1848 exception.

Is there any kind of Oracle hint I can use to force the optimizer to evaluate the subquery first?

Or is there an alternate approach?

Thanx in advance