Your enterprise customer just announced a 14-month migration from on-premise SAP ECC to S/4HANA Cloud. Or NetSuite from a heavily customized 2018-era account to a fresh OneWorld instance. Or JD Edwards to Oracle Fusion. Whatever the flavor, the message to your B2B SaaS product is the same: the integration you spent two quarters hardening is about to become a moving target, and any synchronization failure during cutover will be visible at the CFO’s desk.