https://github.com/geonetwork/core-geonetwork/pull/6972/files#diff-c7548d94bdb4268915f50f66df5a90f1f7868e4fb1de2f3d2938397e202aaf2fR1057
added month and year format support. This was resolving thesaurus date
to the last matching format ie. 1st January for the default date.

This can be tested using regions thesaurus which will contains 2 dates
for the thesaurus block.

#6972 adds retrieval of `dct:issued|modified|created` dates but multiple dates could be added more than one time with same date type code. Improve the mapping.

… errors

No need for duplicated date