Yes but on the same page it admits the forecast can still be lower than the actual levels, as O3 is unpredictable at certain times of year.
It quotes March/ April but there seems to be evidence of unusually low O3 overhead at different times of the year too.
I think you have missed the point. The point was just because they are forecasting on the automated forecasts an 8 it doesn't mean that is what is expected as they automatically rounded it up.
The 8's on the forecast maps or in reality the 7's that have been at times widespread over past weeks will be due to lower then normal ozone above.