Whose standard? Mp3tag or ID3?
In ID3v2.3 DATE is the standard frame name for TDAT.
If I use RELEASEDATE, it merely writes a TXXX/RELEASEDATE frame instead of a TXXX/DATE frame.
So when Florian said:
it's not entirely correct, as DATE or %date% worked as per ID3v2.3 standard in v2.52