The annual updating of the thesaurus with a new edition enables:
- Replacement of terms with more up-to-date terminology
- Replacement of ambiguous terms
- Correction of errors
However, these changes may impact the ability to search previously indexed database records for those who use the thesaurus as a controlled vocabulary. The Thesaurus Staff makes all effort to replace deleted or modified preferred terms with a cross-reference to the new preferred term. There are 210 replaced preferred terms between the 2019 and 2020 editions.