Time period between stories isn't enough to show massive character development, it's much more subtle than that. Kind of like reality. I'm not a hugely different person now than I was a year ago (disregarding time travel, fighting data crickets in sub-space, an endless summer etc) so I don't see how you can expect their character development to go in leaps and bounds.
That said, there is some genuine, enjoyable character development, but the warped chronology and the lack of time between stories makes it difficult to spot.
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