If looking at it that way, abide by the lower weight limit. In that way, you cannot be out of compliance.
However, as many have pointed out, NCL doesn't actually weight anything and even if they did, what proof would NCL have that their scales are (or have been recently) properly and accurately calibrated? 20 kilos, 22.7 kilos, or 23 kilos isn't worth thinking about.
FAQs and the answers given don't hold the same weight (pun) as terms & conditions. Follow what you sign/agree to and you'll be fine.