[@mention:454478741268114544] I think I missed your original question, so I'll back up a bit. You asked, "In other words - can a legacy policy be amended AND [emphasis mine] retained? If yes, can you point me towards proof?" The answer to this is, "no;" they can't. The proof is stated in Section 5.4, "In addition, they [the legacy policies] may not be modified or added to in their legacy form."
With that said, yeah, so in that case you could have A, C, D, E, etc. stored as "legacy policy," but B MUST be captured in governance since it was replaced (and would contradict to have B mean two different things).
Anyone with a role that cares about the confusion of having policies in two different places could also force the early retirement of legacy policies simply by proposing them, as is, in governance. It would be hard for someone to object to that I imagine. And as soon as they are in governance the legacy policy dies ("However, these legacy policies and systems will lose all weight and authority as soon as Governance is defined that replaces or contradicts them.")