Thanks Jim ...
I think at this point we have to consider ascribing any absolute value to the runway surface condition as speculative. We don't have the data and it's hard to know what might be developed in that regard.
From the CVR the tower reports the runway as "wet and slippery" but the term slippery has no specific friction coefficient value that I'm aware of. If it was truly like thin ice (icy = .05 according to Airbus) then there would be more than one A320 and probably a few B737's as well off the runway that night.
The 15% increment for the ground spoilers should apply to all of the normal landing distance numbers that Airbus supplies as long as the actual braking co-efficients match the defined level of contaminant. All bets are off though if hydroplaning occurs or something else drops the co-efficient below the accepted values. In such a case the contribution of the ground spoilers would quite likely be higher, but the total stopping distance would be much higher as well making the over-run probably inevitable regardless of ground spoiler position. The critical question then would be why the braking co-efficient was lower than advised to the crew, not why the ground spoilers were not extended.
The other point would be that if "slippery" does denote a particular relative braking co-efficient that is below wet in Brazil then it would have been incumbent on the crew to consider whether the landing was still within safe parameters, particularly given the inop T/R. Relating to T/R deactivation, my MEL says "Refer to operations regulations for performance on wet, contaminated or slippery runway." (Interesting, there's that word slippery even though it's not defined!). So, specific consideration needs to be given in this case.
For most companies I know of the usual rule is that aircraft with inop T/R's are not dispatched to airports where contaminated conditions are likely to exist principally because contaminated runway takeoff performance usually requires consideration of reverse thrust. Landing performance is also a concern, but it's the inability to do the take-off that's usually the bigger problem.
In any event if there was any question of the runway surface having a braking co-efficient of lower than that defined by a "wet" condition, further discussion by the crew which we've seen no evidence of should have occurred before landing. As you say a CVR transcript of the briefing if available may be key. Were the autobrakes armed? If so, to what setting? If not, then even more pointedly ... why the delay in applying brakes manually?
Perhaps the ground spoilers not being extended played a role, but I'll stick with my concerns regarding the lack of a timely application of the brakes as being the biggest factor subsequent to the initial failure to retard T2.
Only a thorough and professional investigation will tell us about that for sure or about the actual runway condition. Until we know those things we're all just guessing.
ELAC