Hi Alison,
It depends a bit on what kind of auto-completion your are using and how everything is configured.
Funnelback uses 2 main types of autocompletion:
simple/organic auto-completion returns words and phrases from the body of words that make up the search index. This is based off the spelling suggestions index that is built during indexing. Titles may or may not be included in this depending on how the title metadata is configured and whether or not it’s treated as content.
rich/structured auto-completion is based off items that come from CSV data. The CSV data is usually generated either via some custom code and a template, or if you are using a plugin if you are using a very recent version of Funnelback. Suggestions that are generated for rich completion depend entirely on what is configured when that is built. This includes the source of the trigger values and also the contents of the suggestions itself.
If you need specific assistance with your configuration I would probably recommend contacting the support desk with details about your setup.