This would be normal if the files were saved in an earlier version than the one used to open them.
These are files created and edited in CS5. When I open the file, it opens with an asterisk there. Even without making any changes, I am asked to confirm whether I want to save or not. This does not happen with all files I have created in CS5. New documents I start from scratch don't exhibit this. The documents that do are related in that I start a journal's next issue with the old. From then on, each time I open this next issue, it opens with an asterisk. Is it something in document settings ?
There's nothing in document settings that would cause this, but "recycling" files as you describe is likely to build up file correction and eventually lead to failure. Working from a clean template is a much safer course of action. In the meantime, see Remove minor corruption by exporting
Did you have used time based text variables? Those would make changes without editing anything.
Thanks for the good suggestions.
IDML export did not solve the problem. There were no time-based variables.
I solved the problem by brute force. Found similar file that could be opened without the symptom. Narrowed down by deleting pages, then elements. Substituting a similar but different image file ultimately solved the problem. No indication of corruption that I could see.
Now, re-opening the .indd file results in no asterisk!
So the defect slipped in as the original file evolved (I had made changes in the area along the way, but hadn't immediately noticed the asterisk symptom)