In the UK, the Government's Department for Business and Trade (DBT) are the owners of the UK's tariff data. They pass changes to it on to HMRC, who then use it as both the basis of the online tariff, and for validation of declarations entered in CDS.
Sometimes there are instances where the CDS business rules do not properly interpret the tariff measures as they should, which HMRC are working to resolve, but the source data isn't always 100% correct.
To help with these issues, a new Issues Log has been launched to assist declarants to identify these matters before they cause difficulties. If a UK customs declaration has a tariff-related problem, when everything else on the declaration seems correct, this log should be checked for relevant information.
HMRC also provide a list of workarounds for known CDS errors.