The csx572_1404.exe is a full install (226mb). Seeing as all of the gauges (except those only essential to the other 757 III Expansion Models) are in the CS_B757-200-III_PW2037\panel folder, any fixes for the gauges will be there, so there is no need to update the RR's, -300's, or Freighters.

However, what the fixes are, I have no idea.

Interestingly enough, my 757 III's in P3Dv4 never notified me of the update, even though it's available via the Extended Download Service (I never tried it in FSX/SE/P3Dv3).