Given the threat from off-prem solutions like AWS, its not surprising that vCenter lifecycle management was also a high priority for VMware. I mostly worked on the vCenter 6.5 Appliance installation, upgrade and migration wizards. However, I was also involved initially with vCenter HA. The wizards received good feedback from customers, especially the Windows to (Linux) Appliance migration wizard. Interspersed with the actual wizard flow, are some diagrams describing the conceptual model and terminology.
This is what was happening in the backend.
Four separate possible workflows, install, migrate, upgrade and restore. Two separate OVF (Appliance) deployment mechanisms, end-to-end (wizard) or OVF tool.
Stage 1 and stage 2 code bases were separate, so it was important to make sure that the nomenclature was consistent.