My source was magazin 1916 year "Morskoy Sbornik". I think, that it was in news agancyes and simple retyping.
I have many information about WWI from various books and other sources.
Why do you think, that it attack was missed?
Situation like:
1 - submarine say that was hit
2 - magazin 1916 year say that was hit
3 - you say that not hit.

I wish understand you point view simple. It need me for insert in my database submarine attacs in my site.