When you create a new assessment answers from previous assessments will carry forward and the latest assessment will contain all the current answers, notes, evidence.
Information you put into a new assessment does not get copied into previous assessments as each assessment is a point in time.
When is data carried forward?
If the same question is asked in the new assessment scope answers, notes, evidence and custom actions are pre-populated into new assessment.
Does assessment data populate older assessments?
Assessments are a point in time.
When you update an answer, note, evidence or custom action the update is not applied to previous assessments otherwise older assessments would not reflect the assessment at that point in time.
In the reporting feature you can compare one assessment to another by creating a radar graph under the standards section and selecting multiple assessments.