You misunderstand Microsoft's legal argument. They aren't saying that ambiguity in the licenses means that they're in compliance with them. Their argument is that what they're doing is fair use, so they don't need to follow the licenses.
That's the hopeless scenario.
Otherwise, the fair use argument fails to be upheld. Then Microsoft must argue that normally Copilot regurgitates a mixture of patterns from various sources, and therefore the licenses in the training data can be ignored.
To defeat this fall-back argument, we must attack the root of the problem: the moment our code is used in training.
That's precisely what the No-AI 3-Clause License achieves, while otherwise being the permissive BSD 2-Clause License that we know and love.