I e-mailed Marriott about this one and got the following reply:

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Thank you for contacting Marriott Rewards.

The highest status in the Marriott Rewards program is the Platinum Elite level. The bar that you see online should end at 75 nights as there is nothing to achieve beyond the Platinum status; what you are seeing online past 75 nights is the plus part of the 75 + to achieve Platinum Elite. Other than the points and Elite nights that you earn for your stays after 75 nights during the year there is no additional level earned.

Thank you for choosing Marriott.

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