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In the early days of SNOMED, during the period when SNOMED RT and the UK's Clinical Terms Version 3 (CTV3) were being merged, many such duplicate pairs of semantically identical but different concept identifiers were deliberately created: the initial stage of the merger involved adding a new SNOMED identifier for every unique CTV3 code. Where both CTV3 and RT had previously had codes for the same clinical notion, this would therefore inevitably mean there would now be at least two SNOMED codes for the same thing - sometimes in fact more than two, because both CTV3 and SNOMED RT themselves already contained both deliberate and as yet undiscovered duplicates of their own.
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