Screen for duplicate invoices after an ERP migration

Define the migration duplicate population

Migration creates a special duplicate risk because the same obligation can appear as a converted open item, a historical reference, and a newly entered invoice. Define the cutoff, legacy system, target system, entities, suppliers, document types, and migration loads in scope. Preserve the new invoice and capture its supplier, invoice number, date, amount, currency, purchase order, receipt, file hash where available, entry channel, and target document ID. Do not assume the target system’s ordinary duplicate warning can see records that were summarized or stored outside its searchable invoice table.

Obtain the approved migration crosswalk and load reports. Record legacy document ID, target ID, conversion status, open or closed state, balance, and exception result. A missing target invoice may have become an opening-balance line, while a visible target item may carry a generated number rather than the supplier reference. Treat the crosswalk as evidence, not infallible truth. Reconcile counts and values to the migration control report and report gaps to the migration or finance owner instead of creating a replacement invoice from memory.

Normalize identity without losing source values

Normalize invoice references in a review layer while retaining original values. Compare case, spaces, punctuation, leading zeros, prefixes, suffixes, credit indicators, and common OCR substitutions. Also compare supplier legal identity, entity, currency, gross amount, tax, order, receipt, service period, and attachment. A normalized number match can be false when suppliers reuse sequences across accounts. A number mismatch can still be a duplicate after a manual prefix or migration transformation. Explain which fields create the candidate and which contradict it.

Search payment and clearing history in both environments. A legacy invoice may be closed because it was paid before cutoff, yet its target historical record may not carry searchable settlement detail. Obtain the payment reference, value date, bank-supported status, clearing event, and any return or void. A converted open item might also have been paid during a transition window outside the final extract. Do not approve the target invoice because its local status says unpaid. Build one chronology across systems through the stabilization period.

Trace converted, re-entered, and paid documents

Distinguish duplicates from legitimate splits, recurring charges, corrections, and rebills. Compare line detail and covered periods, not only totals. A supplier may replace one invoice with two entity-specific documents, or issue a corrected invoice under the same reference. Link credits and cancellations. If the migration split one document by entity or currency, preserve the controlled mapping and ensure the combined balance matches the source. Do not merge target records simply to reduce candidate counts.

For each candidate, assign a disposition supported by named evidence: confirmed duplicate, distinct obligation, corrected replacement, migrated reference only, payment already made, or unresolved. Finance or the designated process owner approves write-off, reversal, blocking, or release actions. AP can prepare the comparison and hold the newest entry. Keep the candidate pair and decision together. Deleting one side of the comparison removes evidence and makes later supplier or audit questions harder to answer.

Clear candidates with evidence and controlled ownership

Before release, test the final target posting against order, receipt, approval, and payment history. Confirm that a duplicate block or reversal did not remove the valid invoice. Search staging tables, workflow queues, and permitted archives for another pending copy. If the supplier asks for status, communicate the supported invoice and dispute reference through a verified channel. Never reveal migration weaknesses or other suppliers’ records. Record the target document that will continue as the company’s operational source.

Monitor duplicate cases through at least the defined stabilization window. Report causes such as crosswalk gap, late legacy posting, dual intake, reference transformation, missing payment history, or supplier rebill. Reconcile confirmed duplicate value as well as count. An outsourced AP team should receive read-only legacy evidence and explicit escalation routes rather than broad migration administration. Success means each paid or payable obligation has one traceable operational record, not that every similar record was automatically suppressed.

Challenge the screen with transition-window cases

Test the review on a legacy invoice paid after the conversion extract, a converted open item with a generated target number, a supplier rebill received in both inboxes, and a legitimate split by buyer entity. Each case needs a different result. The payment case relies on settlement evidence, the generated number relies on the crosswalk, the dual intake case relies on file and transaction identity, and the entity split relies on commercial source detail. A rule that blocks all four because amount and supplier match would suppress valid obligations as well as duplicates.

At the end of stabilization, reconcile candidate dispositions to both systems and the target ledger. Confirm that every reversal or block has owner approval and that the surviving invoice retains its order, receipt, approval, and payment chain. Preserve the legacy lookup method for later supplier inquiries. Report unresolved crosswalk gaps to migration ownership with document-level evidence. The screen is effective when it explains why each candidate is the same or different obligation, not when it simply produces a large list of possible matches.

Retain query dates and system access boundaries in the evidence. A no-match result is meaningful only when the reviewer can see which repositories, entities, date ranges, and normalized fields were searched. If legacy access expires, preserve approved reports or references before shutdown. This makes later duplicate inquiries reproducible without granting permanent broad access to the retired platform.

Sample cleared candidates after payment runs to ensure a later interface or reload did not reintroduce a suppressed legacy obligation. Record the query and result with the stabilization report so recurrence has a named technical owner and does not become another manual AP workaround.