I am an expert contributor (one of 5) to an excellent website, called MyMedicareAnswers.com, powered by Humana Inc, and here is the most recent article to that site.

If You Want to Change, Now is the TIme to Think
Let’s say that your personal situation has changed, or that you have decided that Medigap is a superior option. Or, let’s say that you want to switch Medigap carriers. While it may be entirely possible, there are some subtle points that require some thought and care. If this is you, then the Annual Election Period (AEP) is the most practical time to consider this, because you will be also be able to enroll in a standalone prescription drug plan, effective January 1, 2017.

Medigap Open Enrollment Lasts Until 65.5 Years Old

Let’s back up a moment. Carriers in your state have no choice, they must accept you. If you apply for Medigap before 65.5 years old, then you can access every Medigap plan available in your state (you must be enrolled in Medicare Part A and Part B). Carriers do have the right to charge more, if you use tobacco, or if your height/weight statistics allow. That said, your application will be accepted.

Special Enrollment Periods Exist

There are a set of conditions, under which you can enroll in Medigap, even if you are greater than 65.5 years old. You may be qualify for guaranteed acceptance under a Special Enrollment Period. The list can be found in Choosing a Medigap Policy, an official CMS publication. Please note that not every Medigap plan is included within the Special Enrollment Periods.

Certain States Have Additional Medigap Enrollment Periods

There are minimum standards that exist at the federal level, i.e. it is true in every state. Further, in certain states, the rules have been expanded, so that you may be able to enroll in Medigap, even if you are older than 65.5 years old, and even if CMS-defined Special Enrollment Periods do not apply to you.

Carriers May Have Different Standards
Let’s say that you do not qualify for any of the situations described in the earlier paragraphs, and that you wish to apply for Medigap. Here are a few things to keep in mind. First, the medical questions and the medical standards used by carriers can differ. We cannot control the questions that are asked. We cannot control the decisions that are made by the carrier. You should be aware that the different carriers can ask widely different questions. For example, some Medigap carriers have extensive questions about diabetes, and some will not.

Second, there is something called a “pre-existing condition waiting period,” which a carrier can imposed if a medical situation was diagnosed or treated for the 6-month period before your Medigap policy is effective. Importantly, this waiting period can be waived if you have had health insurance coverage in the time immediately prior to the your Medigap effective date.

Why Is This Important?

There are many reasons that the different questions matter. Perhaps the most significant reason is that some carriers will ask you if you have been denied by another Medigap carrier. While we cannot control the decision that an individual carrier makes, it is probably does not require a crystal ball to predict what would occur at the 2nd Medigap carrier, if it was aware that an application was already denied at the 1st Medigap carrier. In other words, if you have any risk of being denied, it may be advisable to seek outside assistance in selecting and applying for Medigap outside the Medigap Open Enrollment Period, and outside the Special Enrollment Periods.