Targutai, when you dive into doing things in the API it will help to understand the back end structure of the Pages.
I'll try my best to summarize, but depending on how you have things set up, it will alter what you need to do to set a value on a page through the API.
- Each Node on the Tree has a single entry in the CMS_Tree table, along with that it also will have a CMS_Document entry that represents the language version of that node. Lastly depending on what type of page type it is, it will have an entry in that page type's table (ex content_news) that holds the page type specific information (such as news story)
- If you have a workflow turned on (Publishing and/or versioning) when you save a document, it actually makes a change to a temporary table until it's published or made live, this table is the CMS_VersionHistory, likewise it also has Workflow tables it needs to adjust (CMS_WOrkflowStep, CMS_WorkflowHistory, etc).
This is why, depending on your setup, there are different API steps that need to occur.
So let me ask you, are any of these pages on a workflow (In the Kentico Admin, go to the Workflow module, and see if any have a Scope that cover your documents).
If not, then use the API here. Otherwise look at the links and find the right one!