Interesting. Then I must have been very lucky. In the past two years, I have frequently checked-in early at various ICs without being charged as a Gold or Plat AMB, including IC NY Times Square (11:00 am), IC Hong Kong (10:30 and 11:30 am), IC Grand Seoul Parnas (11:00 am), IC Bangkok (7:15 am).
At the IC Bangkok I contacted the hotel beforehand and asked to get a very early check-in at ~7:00 am. They replied that they will do their best, but can not guarantee it, but also did not mention any early check-in fee.