---
id: DFMOD-C9-POS-003
title: "Export schema evolution is append-only and backward compatible"
product: web
module: digital-form
type: functional
priority: P1
risk: high
status: draft
automationStatus: planned
sourceRefs:
  tsd: PK141
  tsdSection: C9
  tsdScenario: C9.3
  prd: PK141
  jira: null
automationRef: null
lifecycleStatus: active
lifecycleReason: "AI-generated draft from PK141 TSD C9.3; pending QA review."
lastReviewedAt: null
reviewedBy: null
supersededBy: null
duplicateOf: null
blockedBy: null
preconditionRefs:
  - PRE-DF-submitted-report-exists
tags:
  - web
  - digital-form
  - export-report
  - versioning
  - client-portal
  - pk141
  - staging
---
## Objective
Verify exporting across versions keeps existing columns and adds new structure append-only.

## Preconditions
- See [[PRE-DF-submitted-report-exists]]
- And the form structure changed from one version to the next

## Steps
1. Export combined submissions across versions, including non-compound↔compound and single↔subfield transitions

## Expected Result
- Then existing columns are preserved
- And new structure is added append-only
- And incompatible structure yields empty values while preserving old data
- And Question IDs stay consistent per the evolution rule

## Source Traceability
- TSD: PK141
- Section: C9 - Version Integrity
- Scenario: C9.3 - Export schema evolution append-only
- Acceptance Criteria: PRD C.36 Scenario 1-8

## Evidence Required
- Combined-version export preserving old columns + append-only new ones.

## Notes / Gaps
- Question-ID continuity + empty-value handling detailed in DFMOD-C9-POS-004.