Where do the supplier records come from, and how do I fix a wrong merge?

Contact Harmonisation reads every organisation's contacts, matches them on company number, VAT number, bank details, email domain and name, and keeps one golden record per real supplier. Suppliers only reads them; a wrong match is fixed on Accounts → Contact Harmonisation. Related brands (one management, several trading names) are suggested for a person to confirm — never linked on their own.