It actually works the other way around, so assessments from snapshots are pulled through to reports. Therefore any changes you make in a report do not affect the snapshots.
The age bands and refinements that show up in a report are taken from the 'Latest Age Bands' section of the snapshots.
The latest age bands section on snapshots will always be populated with an age band and refinement (if assessments have been made on your account) as it will show the most recent summative assessment for each aspect. So, if you do not have a summative assessment for the term you are in, it will fill the gap with the last term the child had a summative assessment for that aspect.
Does that screen give you the information you are looking for?