When you assign the blocking reasons to the sales documnt type, it wil not reflect on the sales order. The functionality is, if the customer is applied a particular block in master data, and if the same block is also assigned to the sales document type, then system will issue hard error when you try to process order for this customer.
If the block is not assigned to the document type, then you can process orders for the customers, even if they are assigned with the block in the customer master data.
Hope this helps
Regards
Sai
