There is a disclaimer that comes with the e-certs that say that the flights selected that qualify (not all flights qualify!) for the e-cert discount may or may not be the lowest fares for the route and time selected. This is due to on-going availability of lower class fares and also online promotions. So the rule is, check and double check.
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When once you have tasted flight, you will forever walk the earth with your eyes turned skyward, for there you have been, and there you will always long to return.
- Leonardo da Vinci