Currently the credit check is done at sales order header level.
A feature should be implemented to perform that at credit line level.
Specifically if certain parts are on order, they should not be included in the credit line calculation. This because otherwise the dealer will need to wait for the parts to be procured (as they are in backorder) and additional they also get their credit line consumed.
Credit check should be performed only on the lines that are available and that can be delivered to the customer (reservable).
In our company the business is now manually adding the total amount of on-order to the credit limit to get to the correct plafond usage.