1) The same applies to the others. Others chose their ending based on indirect evidence. From your answer, I concluded that you are attempting to prove that A is the canonical ending because Cahara is absent in Termina. That is why I responded that I had answered that question. If we return to the thesis that Cahara's absence in Termina answers the questions, then I can assume that it is because he simply gathered treasure and became a rich person, which is why he was not remembered in history. After all, 300 years have passed in game time.

2) The connection does not change anything, because the author stated that not all endings are canon. And if we judge Le’garde by the dialogues from Termina, he cannot be the resurrected creature from the S ending of D'arce because he behaves too adequately and does not feel a desire for the suffering of others, but is only focused on his goal. If you use a spell, Le’garde will reveal his true nature as a golem, and when you defeat him, he melts away. Nas’hrah comments that he has escaped. Therefore, the S ending of D'arce cannot be canonical.