Last question: why in the SOP for RNAV GNSS approaches there's no guideline in case of "Check IR 1(2)(3)/FM position" message on MCDU whereas there's a guideline for this in case of PRNAV operations?
Well, remember that the aircraft has "figures of merit" to consider the most accurate aircraft position : first, of course, GPS position received for MMR's, after comes the Radio update crossing DME DME, DME ILS....and finally, GPIRS position. So, during the PRNAV the FMS uses the most accurate (MMR), and it's the ONLY allowed source of data on the procedure (at least of all the procedures i've seen).
The use of precise signal is SO important on PRNAV procedures, that all procedures request the deactivation of the RADIO UPDATE option, to ensure that only MMR's data will feed the FMS's.