Who created/last modified a storyline file?

That functionality isn't built into Storyline. SharePoint and BOX (and, I assume, similar sites) can list when a given file was modified and by whom.

Another option would be to include a text box in the file, and have every editor put their name and the date in it whenever they edit the file.

• As needed, this could be a running list to show all editing, or just show the most recent session.
• You could put this text box OFF SCREEN so it would never show in the published course, but would be visible to editors.
  • For example: I sometimes put notes off screen but near the edge of the Title slide. I use a red text box, so the note is quite obvious:

• Of course, the big caveat with this process is that editors have to remember to update the text box...