I installed GPO, of course. Found in the directory two manuals:
GPO Complete Guide to, Notation Edition;
Addendum of Notation Version, which is older than the above.
Reading the Addendum, I noticed that all KS-s are between C2-B2.
Looking into the Complete Guide and looking at the directory of instruments, I noticed that some KS-s begin with C0 (e.g. cello).
Which one tells the truth?