This article has been superseded by the new information site at https://info.orcid.org/documentation/integration-and-api-faq/
ORCID does not remove duplicates based on DOIs or other identifiers. Rather, multiple works added with same identifier are grouped together based on the identifier. This allows the user interface of the ORCID record to not display a duplicate.
For more on how grouping works in the ORCID Record, see Add works: Display.