Thank you for your review!
Not trying to argue with you in any way, but there is actually a fair explanation of why several guards are no-KO.
The reason is that normal guards have their necks exposed, while no-KO guards have their necks covered with metal helmet.
During gameplay, we cannot see that in simplified animations, but Garrett is supposed to knock them out with the neck or lower head hit, and not hitting directly onto the metal helmet.
Thought this could be a nice fun fac...
Nothing is perfect. So are the fan missions.
Don't get frustrated about lower ratings too easily.
Feel free to be frustrated when you cannot find this specific item hidden in the least obvious place.
Rating will reflect not only analysis but also experience (or emotions).
FM authors are not professional (in most cases) and such imperfections are natural thing to happen.
Hi there!
Assuming you are at Calendra's house, you should have "Lady Calendra's Key" with you. This key will open a floor door to the basement.
See the supreme ghosting video (at time 1:04:12 )
https://www.thiefguild.com/videos/18856/lets-supreme-ghost-thief-calendras-cistern-segmented-run-no-commentary
Cheers
Konrad