Continuing on 3 engines is actually fairly common among many operators. On the 744 its just means you cruise a bit lower and reduce range by about 10%. Much of what has been reported on here by spotters and second hand from cabin crew is highly speculative and to the qualified mind sounds like total BS. Continuing on three engines - sensible. Dumping fuel in a non-emergency situation then continuing on three engines - extremely unlikely. Pressing on with grave doubts over fuel levels then only discovering at 3000 ft there's not enough fuel to go around - even more unlikely.