Quite honestly continuity in TV shows seems to be a fairly recent thing in terms of importance. In the past they'd switch up characters visually without batting an eye (the Jimmys for example) while these days there has to be a better explanation as to why they would look different (possibly writing out the character altogether.) TV is much less afraid of rocking the boat than they used to be (just replacing the character physically but not in the scripts.)
When I watch TV shows these days (Castle, Chuck, Smallville, etc.) they are almost predicated on keeping things along a single storyline rather than being able to watch them out of order without a regular problem.
CLARK: No. I'm just worried I'm a jinx.
JONATHAN: A jinx?
CLARK: Yeah. Let's face it, ever since she's known me, Lois's been kidnapped, frozen, pushed off buildings, almost stabbed, poisoned, buried alive and who knows what else, and it's all because of me.
-"Contact" (You're not her jinx, you're her blessing.)
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