Even though an important consideration in the use of standard code categories and procedures is continuity over time, introduction of new or revised codes is sometimes necessary. It is now accepted practice to specify a date of implementation for the new codes. Data collected with outdated codes are often no more useful than old data. For example, to be useful, the AJCC prognostic stage groups require updating as medical technologies advance. Old AJCC stage grouping lacks the prognostic value of the revised codes.