If you choose to delay Pt B. enrollment, your employer insurance co should issue you a letter informing you that the insurance is "Creditable.Coverage" for Medicare purposes. I am sure it will be, but when you go to enroll into Pt b at a later age, you will be asked to provide that information to avoid the late enrollment penality for Pt. b.If your employer is footing the bill for your healthcare insurance coverage and you find the coverage adequate, you wouldn't have to pay the Medicare premium or pay for a supplement until you go off your employer's plan.
My wife's employer offers health care insurance that supposedly covers spouses. They had no clue what their insurance coverage actually was for people 65 and older, however. Her employer referred me to their carrier who didn't even bother to answer me when I asked them to tell me what their coverage actually was. Instead, they transferred my call to someone in their medicare supplement area who tried to sell me one of their supplement policies to which I replied that if they couldn't tell me what the employer plan covered, I wasn't interested in their supplement policy.
My recommendation to you would be to try to get satisfactory confirmation from your employer as to what coverage you would have after 65. Some employers will have an HR department that will immediately be able to help you with your questions.
Also, you may want to read Post #20. Thanks.