Alternate law is a rare failure condition which, by design, does not occur more often than once in 100,000 flight hours
Those requirements, and the special conditions you reference, apply for the airplane systems functioning as designed, without failures.
Seems to me (from the BEA report) that the AF447 was all the way down ( the loss of speed indication was short) a airplane with all systems functioning as designed without failures even in alternate law
Alternate law is not a failure