I have no idea whether your emphysema qualifies for an exemption, but the reality is if you are able to stop taking diabetes meds at any time, your exemption certificate remains valid for the balance of its term. So, if that was 6 months after you received it, or after a renewal, you would qualify for free prescriptions for 4 years and 6 months. Thereafter, you would be reassessed, depending on your overall health, age and so on.
I was diagnosed diabetic, but didn't ever take medication to treat it, therefore I have never qualified for an exemption certificate.
I hope that clarifies for you.