Hi ANonQT,
We understand you have questions about uninstalled apps in cellular data. We're happy to offer some guidance.
The uninstalled apps section would show usage by apps that are no longer on the device. This data would be based off the last time you reset the cellular data statistics. So for example if the last time you reset the statistics was 6 months ago, any apps that you uninstalled during that time would reflect their usage (from the time the statistics we're reset until the time the app was uninstalled) under the uninstalled apps category.
Use cellular data on your iPhone or iPad
Hope this helps. Cheers!