Reckon the go is to do the medical and retain a copy of the Doctor's report. I think that is your right. If CASA are going to deny reissue I think that are required under the Act (or somewhere) to advise you in writing of why they have done so. Anyway that's my argument while I continue to fly without a certificate that I paid for....
It will get interesting when I front the Doctor with no current medical to get the 60 day extension, but whose fault is that? It merely highlights a deficiency in the system.