Silver:
Sorry, but did you read that Powerpoint link? It says (p10), quote...
Indeed, many times. Did you note ANP? RNP is a performance
minimum. ANP is much better on RNP AR approaches or alerting will require the pilot execute an extraction.
As to IRU drift, on any airframe approved for RNP AR of less than 0.30, there are generally three IRUs, with blended position updated continuously by GPS/GNSS. So, if an alert is received that requires extraction, the IRU position is the same as the GPS position was when the alert is received. From that point on (which is very rare) the IRUs begin drifting. This drift is accounted for very conservatively in RNP AR missed approach criteria.
RNP AR is presently the term used for this type of approach throughout the world. The U.S. stopped using RNP AAAR several years ago.