It's your library, so up to you. If you find "Dummies Cooking" more useful, do that.
Note that you can set series to a hierarchical column (Preferences > Look & Feel > Tag Browser > Books with Hierarchical Items) and do something like Dummies.Dummies Cooking. I experimented with this a while back but decided against it.
Also personally I just use a series index of 0 whenever it's non-chronological (e.g. my collection of
Golden Guides).