W3C BibXML no date

### Describe the issue

https://bib.ietf.org/public/rfc/bibxml4/reference.W3C.wot-thing-description11.xml

Besides the problem identified in #473, there also is no date given.



### Code of Conduct

- [x] I agree to follow the [IETF's Code of Conduct](https://github.com/ietf-tools/.github/blob/main/CODE_OF_CONDUCT.md)