Supplier Transition Overlap

Changing suppliers on one day can put service at risk, so an overlap gives the replacement time to learn and demonstrate the work while the incumbent remains available. The period should be intentional, not an indefinite double payment.

Define the scope for each supplier by item, geography, customer or workflow, because if both believe the other is responsible work can be missed, and if both perform it costs and records can be duplicated. Set start and end dates, milestones and objective acceptance tests, since an overlap can extend when testing fails but an extension needs an owner and cost decision, and "until ready" is not a sufficient plan.

A fictional helpdesk moves 20% of calls first and expands only after response times and ticket transfers meet its agreed measures. Project Management Institute guidance on switching vendors discusses transition risks and the value of managing handover, and the CMORG third-party exit-plan template includes transition arrangements for high-impact suppliers, though neither sets a universal number of overlap days.

Check both contracts, since the outgoing provider may owe transition help, charge extra or have a notice deadline, and the new provider may start billing before taking full responsibility. Use a shared handover register covering people, processes, data, equipment, stock, passwords through approved secret channels and unresolved issues, and avoid sending sensitive credentials in ordinary documents.

Data migration needs reconciliation through record counts, sample content, timestamps and attachments as appropriate, because a successful export file does not prove the replacement can use it, as when a fictional payroll team finds some employee records missing from a trial import and keeps the incumbent able to run the next cycle while fixing the gap. A parallel run can test both providers against the same workload, but define which output controls reality, otherwise two systems may create duplicate orders, invoices or customer notices, so a fictional billing transition runs calculations in both systems but sends invoices only from the incumbent until the replacement is approved.

Operational handover includes exceptions, not only routine steps, so document open complaints, late orders, warranty cases and special customer requirements and assign each open item once, as a fictional replacement carrier accepts responsibility for ten deliveries already in transit only after the parties agree tracking and claim handling. Inventory or assets may need a physical count recording condition, location, title and receipt, since a spreadsheet balance alone may not match what moves between sites.

Staff need to know the temporary routing, including which provider receives new requests and which resolves old work, and external communication requires approved wording and timing. Measure performance separately for each supplier during overlap, because a blended service-level number can hide the new provider's weakness, while a common definition keeps comparison fair.

The overlap costs money or credits in some arrangements, so compare dual fees, transition labour and risk reduction, noting that a longer period is not always safer if it creates confusion, as a fictional controller estimates two extra service weeks and checks whether a shorter staged cutover would still allow proper testing. Security and privacy require careful sequencing, as the incumbent may need access for handover but access should shrink as its work ends, with deactivation and evidence of data return documented, so a fictional supplier loses edit access after the last migration check while a limited read-only channel remains for agreed support.

Have a fallback if the replacement misses tests, deciding whether the old supplier can extend, internal staff can cover or orders must pause, and obtain any required approvals before relying on an extension, as when a fictional helpdesk trial fails its call-answer target and the business retains the incumbent for another approved week and records the extra cost. At cutover, confirm a single accountable provider for each live task and reconcile final invoices, open stock, credits and outstanding claims without closing the outgoing contract while important records remain unresolved, then review the transition afterward to note hidden dependencies, duplicate charges and delayed permissions, and update the next exit plan so the same problems do not recur.