The claim relates specifically to the spine 2 project, and is as measured over the 5 years since it went live. There are a lot of systems which depend on Spine 2 for their own availability, it is not the sort of thing that can go down at any time without a lot of people noticing.

I'm biased in that I've been heavily involved in the project, but I will stand by the five years of five nines availability claim.