The certification requirements require the combination of false IRU information and the inability to display a comparator warning be extremely remote(Alf #280 and previous): where -
'Extremely Remote Failure Conditions are those not anticipated to occur to each aeroplane during its total life but which may occur a few times when considering the total operational life of all aeroplanes of the type.'
And
'Extremely Remote Failure Conditions are those having an Average Probability Per Flight Hour of the order of 1x 10-7 or less, but greater than of the order of 1 x 10-9.'
However the particular EFIS design removes the comparator display for pitch values (true or false) greater than 30deg, thus the loss of display and warning is not a combination of two failures but just that of the IRU.
The reported in-service IRU failure rate was less than the required combined value, thus should be considered as not meeting the requirements.