First off: IANAL, so any reader is advised to keep a bucket of salt at their reach.

• Certainly do keep using (c) notices. Just because your work may have protection in their absence, does not mean it is a good idea to drop the notice!^#1 Also, all world is not U.S., despite some who would have you believe so.
• There are several specific forms of copyright, e.g. film subtitles might be covered by some sort of synchronization rights, etc. But in general, only creative expressions are copyrightable. Arranging some elements in a novel and creative way, produces a copyrightable work. Mere idea of such a work, does not. Fixing one typo in a text, does not amount to new creative expression.
• The year number relates to the date of first publication of the work. It is a bad idea to misrepresent the date in either direction. The strength of your copyright claim could depend on its accuracy. E.g. consider a dispute where two parties claim authorship on an expression. An earlier date in such case could mean winning the rights whereas the later publicized work judged a copy. But falsifying the date will undermine your claim. In the other direction, e.g. automatically slapping on a new (c) date 1st January each year, can be seen as an attempt to unduly prolong the status of your work.

So, putting things together. Each significant portion of your distribution has a publication year to it. Keep individual notices in the header of each source content file. List all applicable licenses, (c) notices, years in the distro license text. The purpose of the latter is to inform, and clarity does no harm.

Whether you can use just a range instead of a list, is up to your discretion. In a series of version releases, it is usually pretty simple to show where and when does a particular portion appear.

#1. One good reason to be clear about copyright is to let your users actually make use of your work, i.e. exercise the rights your license grants.