The number of installs on report page is counted according to the install date and time information sent from SDK when an app is opened for the first time.
If you open the app some days after the install, the number of the installs in the pass increase at the timing of that.
- App-Install on January 1
- App-Open on January 3
The install on January 1 is reported when it's January 3. In this case, the number of past installs (January 1) appears to have increased.