In his commentary to Genesis 46:15 Ralbag writes:
והנה מה שאמרו חז"ל זו יוכבד שנולדה בין החומות הוא על דרך דרש וזה שאם היה זה כן היה ראוי שיתפרסם התורה זה המופת שהיה בלדתה משה ואהרן כמו שפרסמה זה בלדת שרה את יצחק כי היה זה נפלא יותר מאד כי היא היתה בת מאה ושלושים שנה כשילדה משה ובת מאה ועשרים ושבע שנה כשילדה אהרן והוא מדרך התורה שתפרסם ענין המופתים כי האמונה בהם היא פינה גדולה מפינות התורה
And behold, that which the Sages of blessed memory said that Jochebed was born between the walls, was by way of derash. And that is because if this [really] was so, it would have been proper for the Torah to publicize this miracle that was in her giving birth to Moses and Aaron, just like it publicized Sarah's giving birth to Isaac. For this was much more wondrous because she would have been 130 when Moses was born and 127 when Aaron was born. And it is the way of the Torah to publicize the concept of miracles, because belief in them is one of the great cornerstones of the Torah.
In his commentary to Exodus 2:1 he says the same thing again and adds that according to his own calculations of the exile and the Exodus, Jochebed would have been 145 when giving birth to Moses. The point that he seems to be making here is that the whole purpose of miracles is to spread the knowledge of God's power, so it would make little sense for the Torah to not mention that a miracle occurred if in fact a miracle had occurred.
In his commentary to Joshua 10:12 Ralbag rejects the view that the sun stood still for Moses for the same reason – had such a miracle occurred the Torah would surely have mentioned it. He reiterates this in Wars of the Lord 6:2:7:
As this was a difficulty for some of our Rabbis because they believed that this miracle did indeed consist in a change of the order of the movements of the heavenly bodies, they maintained that something like this miracle had actually been performed by Moses. But if this were true, the Torah would obviously not fail to mention it, since it is a pivotal point upon which the whole belief in miracles rest.
(Feldman translation Vol. III p. 493)
Similarly, in his commentary to Genesis 18:6 he rejects the view that Lot's wife turned into a pillar of salt, and in his commentary to Numbers 22:21 he rejects the view that Bilam's donkey spoke, because in both of those cases there would have been no purpose for those miracles.
It would seem, then, according to Ralbag, that we generally cannot posit miracles not mentioned in the Torah because a miracle that's not recorded in the Torah almost defeats the whole purpose of the miracle.