PBN Stringency Rules RNAV

If an aircraft is approved for, say, RNP 1 (where it has to be within 1 nm 95% of the time) that does not mean that it automatically satisfies the requirements of, say, RNP 2 (where it has to be within 2 nm.) Although the lateral restriction is less stringent, there may be other factors relating to RNP2 that the aircraft does not satisfy and you cannot assume that these will be met.