Let's say someone writes three novels, two of which are sequels.
The 1st novel establishes the main plot elements that are used in the second novel.
The 2nd novel (the sequel) is written in a manner that it continues from the plot of the 1st novel with the same characters and other elements as an intended sequel, but the author declares that it's not the actual continuation of the plot of the first novel and goes on to state that the 3rd novel would be the official sequel.
(Some background on this could be that the author intended for the 2nd novel to be the true sequel, but rolled back on their decision after generating negative reactions from readers and wanted to create a different sequel that still takes on after the plot of the 1st novel.)
What would the 2nd (discarded) novel then be called?