Compatibility covers whether the product can share an environment with other products and whether it can exchange information with them. The draft gives it two measure families. Co-existence is about sharing resources without harm: memory, ports, files, device access, scheduling. Interoperability is about exchanging and using information correctly. The two are often measured as one compatibility percentage, which hides the difference between a product that runs beside another and a product that talks to it. The environment list is part of the measure: a co-existence result without the other products and their versions is not reproducible, and an interoperability result without the interface and the message set is not either.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.