Gwyneth There is overestimating every year. Everybody knows that, so it could be taken into account. Centre assessed grades are moderated by schools and give the candidates the benefit of the doubt if they're borderline. They don't usually count in final grades. They are much more accurate than any algorithm ever could be. Some people have tried to make out that it's "cheating", but it's not.
The reason that an algorithm was developed was because the government was paranoid about grade inflation, but the coding itself was flawed because it discriminated against pupils who went to big schools and colleges. There were also other flaws, such as not comparing results with all the other data the government has about school improvement and the ability of individual cohorts. This could have all been modelled before issuing the grades and the algorithm adjusted. The exam boards have had five months to do it.
It was based on historical data and insisted on fitting all the current entrants on to a curve dictated by the results at the school/college over the last three years. If there were five or fewer entrants for a particular subject, they were exempt from the algorithm, which favoured very small schools, usually private ones.
Teachers were instructed to rank their pupils in order. This meant, for example, that if even one pupil over the last three years had been awarded a U, then one pupil this year had to be given a U. That pupil might have been the worst in the class, but still have been worth a higher grade, but had to have a U. That's why there are bizarre examples of pupils being downgraded two or three grades. Teachers' overestimation might result in half to a whole grade, but it's highly unlikely that a candidate would be that much lower.
As an employer, I would ignore A level grades if the applicant had subsequently gone on to study for a degree. If I were considering appointing somebody straight from school, I would trust the centre assessed grades more than the algorithm and would interview anyway. Only a handful of candidates - mainly from private schools - have been awarded grades higher than the centre assessed grades.