This is all I could find in ICAO Annex 8:
3.4.1 Manoeuvring loads
Manoeuvring loads shall be computed on the basis of manoeuvring
load factors appropriate to the manoeuvres permitted
by the operating limitations. They shall not be less than values
that experience indicates will be adequate for the anticipated
operating conditions.
Where did you find your quoted factors?
EDIT: AAAAAAAh... just stumbled upon JAR27... stupid me.
JAR 27.337 Limit manoeuvring load factor
The rotorcraft must be designed for –
(a) A limit manoeuvring load factor ranging
from a positive limit of 3.5 to a negative limit of
– 1.0; or
(b) Any positive limit manoeuvring load factor
not less than 2.0 and any negative limit manoeuvring
load factor of not less than – 0.5 for which –
(1) The probability of being exceeded
is shown by analysis and flight tests to be
extremely remote; and
(2) The selected values are appropriate
to each weight condition between the design
maximum and design minimum weights.
EDIT 2: So, according to you statement, where in this article do we find helicopters with teetering-semirigid rotor systems?