Technically doesn't matter. First, according to copyright laws in most countries you do not have to display a copyright notice on a website as it is automatical

Technically doesn't matter. First, according to copyright laws in most countries you do not have to display a copyright notice on a website as it is automatically covered. Secondly, the copyright date is when the work was published. If there have been no updates to the page in 2011 (besides the tweets) then they do not have to change the copyright date. For example, if a book is published in 1980 and never edited the copyright date in the book remains 1980, it doesn't change every year you open the book.