Phase ERP by business closed loops: order-inventory-finance before production-quality. Bad cuts freeze dual-running forever.
Part 1 — Phase-one goal is a month-end-capable loop, not a module checklist.
Part 2 — Production, quality, and APS need stable master data—usually phase two.
Part 3 — Dual-run needs a hard sunset for old sheets or it never ends.
Prioritize verifiable scenarios: main path, auditable permissions/logs, and clear interfaces.
| Decision lens | Common trap or cost | Safer cut |
|---|---|---|
| Phase-one loop | Order-stock-AR | Month-end capable |
| Typical phase two | Production/quality/APS | After master data stable |
| Cutover | Warehouse/org grayscale | Sunset old sheets |
Closed loops beat complete module lists
Include production in phase one?
Only if routings and shop reporting habits already exist. Otherwise production becomes oral reporting with a UI.
How long dual-run?
Two to six weeks per org with named reconcilers. Past two months of mismatch means master data is not ready.
Migrate all history?
Prioritize open documents and master data; archive history read-only.
Stop scope creep?
Every change must name what is dropped; ask if each new report affects the phase-one loop.