So we thought he’d be “eligible”

in Feb or March for Medicare so we haven’t done any research on it. Our mailbox has been filling up with various supplemental policy offers and such. We’ve been stalling on it. Since dh is not drawing ss at this point (we are actually repaying them and he won’t be drawing it again until he’s 66). We also thought there would be a problem because he’s working and has company supplied medical insurance.
So imagine our surprise this week when we received two letters from medicare that start out…

Welcome to medicare…as a new enrollee. The bigger of the two letters goes on to be worded like he’s already eligible.
So…have any of you already been down this path? Are there any pitfalls you can steer us around? Would his work policy be considered a supplemental? I know when I was handling dmils there was a penalty if I didn’t enroll her immediately in part D. Our company provided insurance has rx coverage on it—ie: possibly to cover the required part b? I’m particularly concerned because it is the open enrollment time and must be done by Dec 7, according to the commercials, but dh won’t be 65 until late Feb. I’m already confused.
We need to keep the company insurance because the pay part of my insurance and since I have pre-existing conditions (cancer in 1981 and no thyroid now—graves disease) we can’t afford to give up my insurance which I can’t have if he isn’t insured by the company. We also can’t afford to be paying double insurance, when we all know they won’t pay off double.