What happens to layers that are added after the creation of page definitions?
If you define a page using layer comps or SiteGrinder Tools page definitions, and then you add new layers to the document, you will have to update the comps/page definitions in order for those new layers to be included.
How to update pages:
For layer comps, open the layer comps palette, click the layer comp name, and choose "Update Layer Comp" form the layer comp palette's menu.
For SiteGrinder page definitions you open SiteGrinder Tools from the Automate menu, open the pages panel, select the page definition from the list and click update.