Is credit limit required for overdue hold ?

Hi

We have defined a credit check rule with 'Maximum Past Days due' as 20 days.

Now we have a customer where customer bill to site is 'credit check' enabled however 'credit limit' is 'Null' (which I understand is unlimited).

We have overdue invoices for this customer beyond 300+days. Now when we book the order, order is getting booked without any hold (which we are not expecting).

For customers having credit limit , over due hold is working fine.

I want to understand , is it mandatory to put a value in credit limit to make overdue logic work ?