The difference between adding a trademark category and reviewing it is as follows:

1. Different definitions: Adding a trademark category means that the trademark registrant did not check all categories when registering the trademark. After getting the certificate, you can choose to add a trademark category; or you have selected all categories, but you still want to use the trademark in other categories. Trademark reexamination is a legal procedure in which the Trademark Review and Adjudication Board re-examines the request for reexamination made by the Trademark Office when a party is dissatisfied with the Trademark Office's decision on trademark-related matters.

2. The scope is different: the scope of adding categories for a trademark is relatively small, and you can only choose the categories that were originally checked when registering the trademark; the scope of trademark review is relatively limited, and the trademark registrant is not satisfied with the Trademark Office’s rejection of the trademark registration. If you apply for a trademark that is not published, or if you are dissatisfied with the Trademark Office's decision to cancel a registered trademark, you may submit a review to the Trademark Review and Adjudication Board.