It would matter in terms of the world backdrop. It would matter if you wanted to RP a White Council wizard, a Fae, a Vamp, or someone connected to any of the above. So yeah, it would matter.
This is significant, and illustrates a potential snag that can occur in any RPG based on a book/movie/TV show type setting. (And it's perhaps magnified somewhat when that work is still ongoing by the author.)
I think I first discovered this effect back in the 1970's when my gaming group created a
Star Wars campaign based on the only
Star Wars movie released at that point -- our campaign took place right after the movie and made certain assumptions as to where the plot should go and how the characters would develop. We had no way to anticipate that George Lucas would make some unusual plot twists along the way, so our campaign ended up looking nothing like the later movies.
This doesn't have to be a problem, but it might be to some. Suppose the "default setting" for a campaign is after Harry book #5 (just to pick a number at random). Even if PCs aren't plaing the roles of Harry or Murph or Michael or other major characters, what happens in the books and what happens in the campaign probably will be nothing like one another, and if the GM is willing to allow for major characters to have changes (death, etc), then the potential is that future books events might be incompatible. Even in the event that something happens to a minor character, it may be that this character could evolve into a different role by the time Jim writes book #9 (or later) and again an alternate timeline is the only solution. Each individual GM will have to resolve these issues.
As a game designer, the problem I might have to face would be whether to have a "default setting" or not. Where this becomes important is for any character who might have a significant change. Do you include a "Susan before" and a "Susan after" NPC stat block, or do you select one with the assumption that the GM will use it or create his own. Many characters will be essentially the same throughout the series, but a few evolve enough where this should be a consideration.
Just my two cents.