I Am not sure you understand my question: how do autoimport decide which images are new?
i Made an experiment
1. I manually imported all images from camera roll to lr mobile
2. I took 8 photos with my iphone
3. I transferred them to my ipad camera roll using an app called photosync, but any transfer method gives the same result
4. Open lr mobile, and checking the image count in my camera roll collection: nothing imported
5. Waited for 10 min to see if anything happens, but no
6. Disabled and then enabled autoimport again, no activity
7. Took 1photo with the ipad camera
8. Opened lr mobile and that photo was immideatly imported