This indicates that DTM is being used and which code version is being referenced. Here's the schema and an example:
Example: 'D4MS'
'D' for DTM
'4' for 2014
'M' for 'Oct' (also indicative that it's the 2nd revision of the code on this day. If it were the first revision, 'A' would have been used instead of 'M')
'S' for 28
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