Ret Con-ing

One of the main aspects of LOST (and something that makes the show interesting) is that things we saw in previous seasons can suddenly make sense in light of new revelations. Here's a simple example: Minkowski the radio guy on the Kahana starts getting nosebleeds and eventually dies. We have no idea why until the episode The Constant, where it's all explained. Other examples are the polar bear Sawyer kills and why Kate is rubbing her wrists just after the crash in the pilot episode. 

There are two ways to look at this phenomenon; the first is that the writers had it planned all along. When they introduce Charlotte at the beginning of season 4, they have her smile at finding the polar bear skeleton because they've already written that she spent a lot of her childhood on the island and is trying to find her way back.

The other is that these are Ret Cons, or examples of Retroactive Continuity. The writers use a new revelation to explain something unexplained in the show history because it works, not because they had it planned out the whole time.

I think there are examples of both on LOST.  

How do you see it?