I recently encountered an issue where EPiServer Composer appeared to be serving up old versions of pages, even after they have been published. This was identified on EPiServer CMS 6 R2 and Composer 4.
The issue was traced to a particular behaviour where editors copy/pasted a Composer page that contained global Composer blocks. After this operation the newly created page would revert back to an "old" version that contained no Composer blocks. This happened after a period of time and to compound the issue it is only noticable in view mode and not edit mode.