I have looked at the different entry types of biblatex in http://mirror.easyname.at/ctan/macros/latex/contrib/biblatex/doc/biblatex.pdf (p. 8ff, 2.1 Entry Types). Here, I have observed that some entry types define that either the entry field "year" or "date" (year/date) is required. Contrarily, JabRef only shows the entry field "date" as required. The entry field "date" is only shown in "Other fields". This can confuse some users.

One example:

Entry type: article
biblatex: Required fields: author, title, journaltitle, year/date
JabRef shows the following entry fields as required: author, title, journaltitle, date

This could also lead to a problem, when pasting references, where only year={yyyy} is set.

Maybe it could be defined more clearly in the required fields, that either the field "year" or "date" is required. (Of course I see, that the date also includes the year.)

Affected entry types are:

article, book, mvbook, inbook, booklet, collection, mvcollection, incollection, dataset, manual, misc, online, patent, periodical, proceedings, mvproceedings, inproceedings, report, thesis, unpublished

Furthermore, for the entry types:

• "misc" the following is defined as required: author/editor, title, year/date
  • But in JabRef required are: author, title, date
• "online" the following is defined as required: author/editor, title, year/date, doi/eprint/url
  • But in JabRef required are: author, title, date, url