Update
I think the release updates info to include the recon of the Fuel system and to announce that Boeing are now looking for "abnormal combination of parameters." (Having found no one "hole")
It's important to reconsider that "exceeding spec." does not qualify a Fuel as "superior" in quality. It is an easy mistake to make, but "exceed" means "beyond" as well and includes a description including "poor", "misses the mark", and suggests that whatever is present in the fuel may be degrading its quality and performance.
An FP of -57C can be acquired merely by adding light molecules. Acetone freezes lower than kero, as do any number of easily added off spec matls.