inchy, even if the cohort hasn't changed, the phrase "no longer coasting on cohort" could mean they are now aiming to differentiate better.
For a school to get an outstanding grade these days, the bar is much higher than it used to be (so do check dates on Ofsted reports) - the majority of children need to be making outstanding progress no matter what their starting point, and all identifiable groups (e.g. high attainers, low attainers, SEN, FSM, boys, girls) need to be making outstanding progress too.
In the meantime, the national system for measuring progress has been stripped away, and schools/trusts have to put their own systems in place. Some will be further down the road with that than others. It's not an easy time for schools!