De-Risking Big-Bang ERP Cutover: A Rehearsal-and-Reconciliation Discipline for Coupled, Multi-Company Environments

ERP modernization in operationally intensive businesses couples the ERP to warehouse, transportation, tax, payroll and partner systems, so any replacement is a change to shared infrastructure. Practitioner guidance generally favors a phased migration over a big-bang cutover. Yet when the replacement is driven by cost reduction and by the consolidation of several legal entities onto one platform, a prolonged phased transition — running two ERPs and two license streams at once, building and then discarding bridge interfaces, multiplying hybrid states — can undermine its own business case. This working paper reports a big-bang ERP cutover across three legal entities in a nationwide telecom-logistics operation, executed in a single production day with no unplanned operational outage, inside a wider program that finished about two months ahead of its twelve-month plan and cut total ERP platform run cost by roughly 20%. It defines the discipline that made the cutover safe: 1. Full-scale rehearsal — the entire cutover (every module, every legal entity, every integration) is run end to end in a dedicated staging environment, repeatedly, until a clean round is achieved. 2. Numeric reconciliation as the go/no-go gate — closing balances for accounts payable, accounts receivable and the general ledger are compared between the legacy and target ERP after each rehearsal, and the production cutover proceeds only when every department reconciles in the same round. 3. Fiscal-boundary timing — the cutover runs at the annual fiscal year-end close, so the target ERP is loaded with opening balances rather than a year of in-fl In the same program the integration tier wast read source databases directly and loadedthe ERP through custom function modules, into versioned service endpoints on the target ERP; the warehouse andtransportation systems, previously not conneintegrated with it for the first time, andinventory processing time fell by approximately 40% through perpetual inventory control the incumbent ERP did notprovide. Two unrelated post-cutover problems are reponce of electronic fiscal documents forproduct-kit sales, and an underestimate of consolidated document volume that interacted with a SaaS deployment model. The paper states the discipline as three mecance criteria, so other teams facing the same constrained choice between an expensive hybrid phase and a high-stakes single cutover can check an implementationagainst it.