As this Standard and external coding schemes are maintained, the codes specified as Values for Attributes and in Conditions may change. The previous codes are considered Retired but implementations may continue to send them and receivers will be expected to be able to continue to recognize the Retired codes, including the Code Value and Coding Scheme Designator, even if the current Standard does not publish them.

A notable example is the change throughout the Standard from using "SNOMED-RT style" code values with a Coding Scheme Designator of "SRT", "SNM3" or "99SDM", to the use of SNOMED CT numeric code values with a Coding Scheme Designator of "SCT". Those retired codes may be found in PS3.3-2019a. A mapping of retired to new SNOMED codes is found in Annex O “SNOMED Concept ID to SNOMED ID Mapping” in PS3.16.