You have listed 3 examples which I will address them 1 by 1.
1) Filing an application and its being accepted by USCIS, it does not necessarily guarantee the application is approvable. So in the example of USCIS memo, it is possible the 2nd I-485 is ultimately denied for not being in legal status which is omitted in memo since it is not relevant to the point of example.
2) and 3) are merely interpretation of immigration practitioners, so I will not rely on for own sake.
I might be wrong to make 245(k) too tight on reliefs, however I will have to stand on it unless USCIS makes explicitly statement on relief of legal status requirement. The argument might be ruled in your favor which I believe it would be a big burden removal to applicants, by USCIS or IJ, or BIA, by an example, or a case which are still in search.
