Schools will definitely be able to have grades that are higher than usual if they match the cohort's prior attainment ability so if the whole cohort is a higher achieving cohort that will be taken into consideration as will outliers. The underlying policy is an holisitic approach with grades being assessed and students being given what their teachers believe they would have achieved. The main thing that parents need to remember is that predicted grades are not the same. Predicted grades are (can be) the most optimistic grades that the child may get, on a good day, with the wind blowing from the East etc. Predicted grades can often be inflated by schools so that a pupil can apply to an aspirational uni but hopefully the school would have added the provisio to the pupil/parents that they have done that but a more realistic prediction is eg. AAB rather than AAA so that they also apply to realistic prospects. As long as people take that on board and are realistic in their expectations then there shouldn't be too many issues.
However, the schools are not going to be measured on their grades achieved this year and there will be no league tables for comparison and I would be surprised if any school was going to release press releases saying our best year ever and so on as they would be ripped to shreds.