The clause separates two questions. Model evaluation compares predictions on test data with the actual labels and reports the metrics the tools group defines. It warns that comparing many models on test data overfits the hyperparameters to the test set, so comparative evaluation should be limited to a few genuinely different candidates. System validation is a different check: whether the trained and deployed model meets stakeholder needs and whether the assumptions about the environment behind the features were correct. The clause says explicitly that system validation is not the same as validation data.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.