It's not just a question of instrumental error though. There are also assumptions being used in interpreting the data from the instruments, and it's not generally possible to assign them reliable probabilities.

e.g. the first line of the article's abstract quoted above:

"Supernova (SN) cosmology is based on the key assumption that the luminosity standardization process of Type Ia SNe remains invariant with progenitor age."

If the results reported in the article are right, the confidence we should have in this assumption, and therefore any results relying on it, have just radically changed.