I've seen some websites that use the second option, i.e., 2009-2010, to indicate that not all of the work was created in 2010.

[I can think of a similar situation: when old music albums are reissued with bonus tracks and/or remastering, the copyright reflects the original year the album was released, plus the year of the reissue (not all record companies do this, though). For example: "© 1975, 2009, X Records." This, to me, is the best way to go about it, as it lets you know the original release date, and that you are looking at a reissue.]

In the websites I set up, usually I wrote the year of first publication and, after an en-dash, the current year (automatically inserted via php). Just to stay on the safe side.

If a piece of work was created in 2009, then the copyright date for that piece is 2009. It doesn't change just because the year changes. If you want a blanket statement that covers all pieces, then you can either use an en dash for a continuous range or a comma-delimited list of applicable years.