Documentary proof and historical inference

Why are claims about Japanese sextuple torpedo launchers treated cautiously?

Destroyed Japanese records leave strong circumstantial cases without a surviving smoking-gun document, so a historian can label an inference on video but needs firmer proof for a book.

The loss and destruction of Japanese records leaves gaps in which technical evidence may point strongly toward a conclusion without proving it directly. Such an inference can be explained aloud as a strong suspicion. Formal publication demands a hard document that can be cited, illustrating the different evidentiary burdens of discussion and scholarship.