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When you edit a question, by default, it won’t impact any running assessments. This is because questions are snapshotted every time a new assessment gets created. This is import for maintaining the integrity of assessment data. If you edit any aspect of a question (including the question itself, the answer response group, weight value, etc) and you want those edits to impact active surveys in a running assessment, then you need to update the snapshot for that assessment. If you update snapshots for the assessment, then ALL changes that have been made to any included questions will get pulled into the snapshot for that assessment, and any impacted portions of the assessment will be unlocked and have to be reviewed.
See also: DRAFT: What are question snapshots and why would I update them?
Once an assessment has been completed and finalized, you can no longer make any changes. If you realize that you have an erroneous question in a survey that was already finalized, then you will have to create a new assessment using the new version of the question and start over.
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