Neither of your statements are what was reported. What was reported by Jeff Goodman is that Danny Manning signed a six year contract extension through the 2024/2025 season. The reported value of the contract was around $18 million and it was fully guaranteed.
It would make sense that Danny's contract year would be May 1 through April 30. Hence, Wake would have owed Danny $18 million if he was fired last spring.
Wake has been paying on the contract extension, probably since May 1, 2019 and reducing the "buyout" by each payment.
Simple arithmetic of 72 months of extension and $18 million means that each month of payments reduces the remaining balance due by approximately 1/4 million dollars.
That would mean that the approximate remaining amount owed would be $16 million as of Dec 31, 2019. At the end of April, the remaining value would be about $15 million. As time passes, the remaining value (and buyout number) will continue to decrease.
All the numbers are approximate because the original $18 million report was an approximate value and we have no information about the distribution of payments over the years. The annual payment could be lower this season and higher in the 2024/2025 season.
The only thing acknowledged by Wake is the six year extension.