That does not rule out central banks being more transparent about their estimate of the unemployment rate that is consistent with maximum sustainable employment, though no central bank has ventured into this territory. That's perhaps not surprising.
Indeed, it would be difficult to do so because there is considerable debate – both inside and outside central banks – about the usefulness of a "full employment rate of unemployment" as a guide to policy and, even among those who believe this is an important and useful concept, about what that rate may be today and how it tends to change over time.