Personal data is inaccurate if it is incorrect or misleading as to any matter of fact.

If you discover that your personal data processed by CERN is inaccurate or incomplete, you should request its correction or completion by providing the necessary evidence, for instance justifying documents such a copies of certificates containing the personal data concerned.

It is the duty of the Controlling Service to keep the personal data accurate and to rectify the data if necessary.

Whereas it might be relatively easy to determine if facts, such as a maiden name or a birth date, are correct or not, in cases where the data in question records an opinion (for instance a letter of recommendation or a medical opinion), it may not be obvious to say that it is inaccurate and needs to be rectified as opinions are, by their very nature, subjective.
As long as the record shows clearly that the information is an opinion and, if applicable, whose opinion it is, a correction will not be possible. Where appropriate, the Controlling Service can propose you to submit a counterstatement and to add it to the file.