I have made a small personal study on this subjectmatter of the undeclared points.
Many people know that the Buddha did not declare : the Tathatagata exist, not exist, both exists as non-exist and nor exist nor does not exist after death . He also did not declare about the soul and body , the world. Many sutta’s give the reason why: it is not conducive to the goal, it does not lead to dispassion etc.
But i have seen that it would be a mistake (in my opinion) to think ‘undeclared’ means the same as ‘undecided’ (or unknown or left aside).
Take for example SN44.4, two fragments:
“Reverend, not truly knowing and seeing form (and the other khandhas, Green) its origin, its cessation, and the practice that leads to its cessation, one thinks ‘a Realized One still exists after death’ or ‘A Realized One no longer exists after death’ or ‘a Realized One both still exists and no longer exists after death’ or ‘a Realized One neither still exists nor no longer exists after death.’
"Truly knowing and seeing form … feeling … perception … choices … consciousness, its origin, its cessation, and the practice that leads to its cessation, one doesn’t think ‘a Realized One still exists after death’ or ‘A Realized One no longer exists after death’ or ‘a Realized One both still exists and no longer exists after death’ or ‘a Realized One neither still exists nor no longer exists after death.’
So, i feel, one cannot say that this matter is really undecided or unknown or left aside.
Especially in SN44 much deeper explanation is given why the Buddha did not declare about the status of the Tathagata after death, about soul and body and about the world . There is much more said then that is not conducive to the goal.
In my opinion it comes down to: still thinking in this tetralemma like way, is still a sign of ignorance, not really seeing and knowing.
So, i have for myself concluded that ‘undeclared points’ is not the same as undecided points.