The CMS allows only four exceptions to timely filing. They are as

The CMS allows only four exceptions to timely filing. They are as follows:

1. Administrative error. This is seen when there is a misrepresentation from an employee, the Medicare contractor, or an agent of the department. If that is the case, timely filing will be extended by six months from the month you or the beneficiary received notice that an error or misrepresentation was corrected.
2. Retroactive Medicare entitlement. In this case, services are rendered to an individual who is not entitled to Medicare, and later the individual is notified by the Social Security Administration that they are entitled to Medicare benefits retroactive to a date on or before the date of service.
3. Retroactive Medicare entitlement involving State Medicaid agencies. In this case, the patient was entitled to Medicaid, not Medicare, at the time services were rendered. Later, they are notified that they are entitled to Medicare. You may be given an extension to file claims to Medicare if the State Medicaid agency recoups the money it paid you six months or more after the date of service. But to qualify for this exception, you must provide documentation that verifies the service or services rendered, the date of the service, the date the State Medicaid agency recouped money from you, and that the beneficiary was retroactively entitled to Medicare on or before the date of service. If this exception is met, timely filing will be extended six months from the month the State Medicaid agency recouped its money.
4. Retroactive dis-enrollment from a Medicare Advantage plan or Program of All-inclusive Care for the Elderly (PACE) provider organization. This occurs when a patient who is enrolled in a -Medicare Advantage plan or PACE provider organization later becomes disenrolled and the Medicare Advantage plan or PACE recoups their payment.
Source:

https://www.cms.gov