At the time of creating a Sales Order or maintaining it a credit check is run.  But if you do not run the auto credit check then it will  stay that way until you change it manually.  so for example you create a SO a few days ago but it gets put on hold.  Then the day after you get a payment from the customer so now he has more available credit.  When you create the new order it will pass because at the time of creating that order there was sufficient credit available.  If after receiving the payment you had run  the auto credit check the older worder would have been released and the new one would fail.  Many years ago I created a program that was run each night and did a series of checks.  For example if there was a zero price on a line but it was not marked as a sample order then it would use a credit hold code of ZC (Zero Cost),  It went through many different scenarios based on what this client needed.  It would also release any that now matched all conditions and had available credit.  Another feature we built in was if the order total was below a certain amount then it would put the order on hold.  However, this was a much older version of QAD but in reality a lot of these checks are still valid.