Is there any meaningful documentation of the possible values of the FAXERROR and FAXSTATUS variables and the relationship between them?

I have seem combinations where FAXERROR has come back as NO_ERROR, but FAXSTATUS has indicated that the fax has failed, e.g. a combination of FAXERROR=NO_ERROR and FAXSTATUS=FAX_FAILURE_PARTIAL and I can not say for sure whether or not the fax has delivered.
I tend to treat FAXSTATUS as definitive and FAXERROR as additional information, but I would be more confident if I could find proper documentation.