It is updated on each edit on the mobile, but only stored as a single history entry on every sync. This means that if you edit the data without syncing, it will just update the same record on your device. Once it’s synced, a history entry will be created on the server. If you then change it again on the device and sync, it will create a new history record on the device without losing the old one.
For example, the device is at the field and all the values are captured, but then when our field person is at home, they notice something they missed and enter the missing value at home.
The last location (home) would be stored. Depending on if they synced before editing at home, you will be able to see the field position in the history though.