Not all attributes appear in Searchable Attributes

I have an index where I defined a set of Searchable Attributes. I added some new data that had some new attributes. Those attributes do not appear in the Searchable Attributes drop down. So I dropped the index and reloaded it. Now only the attributes in the new records appear in the drop down. Apparently they happen to appear at the beginning of the index. How do I get all attributes to appear in the drop down?