Overlapping data is handled based on which Abbott Diabetes Care devices are being combined:

Between app and reader – App data will be presented instead of reader data in most cases, except for when there is a reader for more advanced sensors.
Between two Apps – Data from the App with higher priority will be presented. If the Apps have equal priority, data from App having the most recent data will be used. If the same timestamp, the App with the most data has higher priority.
Between two readers – Data from the Reader with higher priority will be presented; if the Readers have equal priority, data from Reader having the most recent data will be used. If the same timestamp, the reader with the most data has higher priority.
Note: some devices and mobile apps may not be available in your country/region.‎

Note: Notes from all devices are displayed without modification. If the same note is entered on multiple devices, all instances are displayed. Data uploaded into LibreView prior to the release of version 3.0 cannot be merged.