(a) defects in the delivered goods, property, or services;

(b) defects in the invoice; or

(c) suspected improprieties of any kind.

The existence of such defects or improprieties will delay the commencement of the time period specified in section 801.4 of this Part until such defects or improprieties are corrected. Notification to contractors under this section must be in the form of a standardized letter. If the corporation fails to notify a contractor of such defects or suspected improprieties within 15 calendar days of receiving the invoice, the number of days allowed for payment of the corrected proper invoice will be reduced by the number of days between the 15th day after receipt of the original invoice and the day that notification was transmitted to the contractor. If the corporation fails to provide reasonable grounds for its contention that a defect or impropriety exists, the date by which the contract payment must be made in order for the corporation not to become liable for interest payments will be calculated from the date of receipt of a proper invoice.