It was always my understanding that Reb Moshe David (Tendler) was the one
who edited Reb Moshe's teshuvos and that there are many teshuvos that are
still unpublished. Also, the two Rabbanim who put out the new volume are
Reb Moshe's grandsons - Reb Mordechai Tendler (Reb Moshe David's son) and
Reb SHabtai Rappaport, both who are bekiim in the Igros and were meshamesh
R' Moshe and understood the reasoning behind the teshuva as well as all
details of the shaila (Rabbi Tendler once said that the problem with
people learning the Igros and trying to get their own psak from it was
that they didn't understand the question). Keeping this in mind, I don't
see why Akiva Miller has a problem with the fact that new volume(s) came
out after Reb Moshe was nifter [passed away].
Steven A. Perel