Help converting YEAR field YYYY-MM-DD to multiple fields in Mp3tag for FLAC files

[ohrenkino]

AFAI can tell it does not make sense to map RELEASEDATE to RELEASEDATE (the same applies to most other fields with the same source and target).
Could you remove (at least) this mapping and see which fieldname you really get?
See e.g. this thread about Mapping

How to map ALBUMARTIST TO ALBUM ARTIST for flac files

Using Mediamonkey and Mp3Tag-mapping you would have to create a mapping pair like this: Tag: Vorbis Comment Source: ALBUM ARTIST Target: ALBUMARTIST So every flac file in Mp3Tag shows ALBUMARTIST if their is a tagfield "ALBUM ARTIST". But it also shows 2 ALBUMARTIST fields if there are "ALBUM ARTIST" and "ALBUMARTIST" in the tag. The mapping is very useful if your are working in Mp3Tag across different formats (i.e. MP3 and FLAC). Without defined mappings you would have to create different …

The field list is no reliable indicator that a field is a standard field as it fills up with all the field names that have been used before. You would have to reset the field list for a more reliable picture.