Business integration is no longer optional. With the opening of local and world markets to international competition, businesses have been actively looking at managing their costs, their competition, and their customers' expectations. Integrating business processes amongst partners was deemed as an efficient way to meet these objectives. Amongst various concepts, Inter-Organizational Information System (IOIS) has seen a significant interest from organizations and researchers alike. IOIS is an inter-partners information system that enables adding seamlessness to business processes crossing these partners' systems. The component inside IOIS responsible for the bridging between different partners' systems is the InterOrganizational Middleware System (IOMS). IOMS is both a technical tool managing communication and data exchange between heterogeneous systems and a business tool proactively participating in the business process. This duality has been a strength but also a problem for IOMS. Indeed, organizations tend to resist updating and upgrading it and in the process causing it to suffer the problem of legacy processes. When these legacy processes become unupgradable, i.e. can no longer be updated using standard methods and tools, the risk to business increases and the cost of keeping these processes functioning becomes excessive. The authors embarked on a four-year journey investigating the problem of Unupgradable Legacy Processes (ULP) in IOMS and propose numerous artifacts addressing various elements of the issue. Riding on these artifacts, this paper looks at their journey from an implementational perspective and assesses lessons learnt for organizations to both manage and avoid ULPs. First, the concept of IOMS is presented. Then the problem of ULPs in IOMS is discussed. Research findings are then presented as lessons learnt before the outcomes are analyzed and limitation of the research are debated.