Actually the NAR does make the distinction that model rocket motors with an average thrust > 80 NS of thrust are also considered high powered rocket motors requiring the person to be at least 18 years of age and to also be certified L1.....
There is of course a loophole in the NFPA Code for High Power Rcoketry that allows a person 18 or above to purchase 1 HPR motor for certification purposes but of course although a F101 or Gxxx is considered a HPR motor, you can only cert L1 with an H or I.....
I might add that the CSPC, Consumer Safety Product Commission also uses this definition......As does the NFPA codes that the NAR/TRA helped develop.....
I don't know why the NAR does not include this information on their website..... or why NFPA 1122 Code for Model Rocketry does not also contain this....It is contained within NFPA 1127:
3.3.17.1 High Power Rocket Motor. A rocket motor that has
more than 160 N-sec (36 lb-sec) but no more than 40,960
N-sec (9208 lb-sec) of total impulse, or an average thrust
greater than 80 N, or more than 62.5 g (2.2 oz) of propellant,
and that otherwise meets the other requirements set forth in
NFPA 1125, Code for the Manufacture of Model Rocket and High
Power Rocket Motors.
from CSPC 1500.85 :
(8) Model rocket propellant devices
designed for use in light-weight, recoverable,
and reflyable model rockets,
provided such devices:
(i) Are designed to be ignited by electrical
means.
(ii) Contain no more than 62.5 grams
(2.2 ounces) of propellant material and
produce less than 80 newton-seconds
(17.92 pound seconds) of total impulse
with thrust duration not less than 0.050
second.