It was tricky enough to work out age and mileage with some people's thread inputs! I chiefly did it to try and prove/disprove my previously expressed theory that failure was age- rather than mileage-based, but I think the jury's still out.
Perhaps we can surmise that the transfer box 'usually' fails after the 12 month point and irrespective of mileage. The second failures maybe statistically irrelevant, and potentially due to poor replacement/modification.
Given that it is reportedly a 'breather vent' issue, a more comprehensive analysis would look at how the car was used, stored, washed (jet-wash?), garaged, etc. Porsche themselves would be well placed to gather this data but I doubt that they care as long as it lasts the initial warranty period with just one replacement, and furthermore encourages the gullible owner (me!) to take out a lucrative extended warranty.