Quote:Ranma (and a number of other series) take place in Riverdale Time.
Ranma on the other hand is almost timeless.
That is, it is ALWAYS Ranma's first year of high school. He is always in the same class as Akane and Ukyou. Nabiki and Kuno are always on year ahead of him and both still in high school and so on. It is noteable in the manga that new years passes... TWICE and yet no one ages or graduates. This despite the fact that the Japanese school year ends in winter. The seasons change to reflect the season that Rumiko was epxerincing when she wrote it, not when it should. Ranma goes through summer vacation at least three or four times.
Other series are more definitive. We can pretty much place the Read or Die OAV series at a specific moment in time (around 2000 or so) and the follow up TV series follows up on it a specific number of years later. Harry Potter, as you said, takes place over the course of seven years staring when the first book was published and working their way up from there. Buffy the Vampire Slayer starts the year it started and ends the year it ended.
That being said, adjusting timelines is not really a big issue unless it would ruin the story to have a major technological or political advancement which would render the story moot. For instance, you could not reasonably set The Hunt For Red October in 2006, because the political situation that existed when the story was set no longer exists. Similarly, Indiana Jones can not be set in contempary times because the existence of GPS and hypersonic jets makes a lot of the "exotic travel to unexplored lands" aspect suspect.
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