I believe that calculation would give a total refund for unused days but that doesn't match what Disney seems to be offering, max 117 days less any days that would have been after expiration during closing.
Some have said they've asked Disney for a bigger refund to reflect all unused days (your calculation) before March 15 and that seems to be case by case.
What is unclear, at least to me, is how this new extension is being managed and what options will exist if declining the one month.
see:
Alternatively, and in lieu of the one month extension, Passholders who have paid in full may choose to cancel their annual pass and receive a partial refund.