If at the time disclosures must be made, an amount or other item of information required to be disclosed or needed to determine a required disclosure is unknown or not available to the creditor, and a reasonable effort has been made to ascertain it, the creditor may use an estimated amount or approximation of the information, if:

   (1)   The estimate or approximation is clearly identified as such, is reasonable and is based on the best information available to the creditor; and

   (2)   The estimate or approximation is not used for the purpose of circumventing or evading the disclosure requirements of this subchapter.