I'm currently debating what constitutes a bug and a story. 

1. If there is no evidence for expected behavior then, Are all perceived issues are bug?
2. If a change is made in a story that wasn't detailed in the criteria of the case, is that a bug?
3. Is any additional change not specified in a case a story? Even if it seems like a bug. e.g. is so obviously wrong that the oversight in the case should have been spotted.

How far should you go with this train of thoughts? It feels overly pedantic but I'm trying to weigh up the benefits of being more rigid with the propositions above.