One of the many common abbreviations used in research reports is 'n.d.'. It means

The abbreviation n.d. stands for no date in research references.

It marks a source whose publication year cannot be determined.

It is placed where the year would normally sit in the citation.

No data, no details and non descript are not what this abbreviation denotes.

Each of those wrong expansions confuses missing figures or description with a missing year.

The related term et al. means and others for multiple authors.