I don't want to state the obvious, but if Locke took some of the C4, that means that the entering of the number 77 into the computer was NOT a self-destruct trigger. 77 was simply notifying the Dharma Powers-that-be that the station had been overrun.

It also means that Locke probably set the rest of the C4 to explode after he left.

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charlie98210
"Whoa!" she said. "Cry 'Havoc!' And let loose the dogs of war!"
And, like Banquo's ghost, they just won't go away.