You should always try to find a date for your sources. Most reliable sources of information will have a date - either a date for when the source was published, or a date for when it was last updated.
For books:
If you genuinely cannot find a date, and you must cite this work, use "date unknown" in place of the year.
- Brown B. Self published books are the future of science. Brown's Own Books; date unknown.
For websites:
If you genuinely cannot find a date, and you must cite this work, omit published date and use the updated date and date accessed.
- Smith J. Carrots can cure everything. Carrots Marketing Corporation. Updated June, 2014. Accessed May 25, 2015. https://www.fakeurlforexample.net.au
- Jones L. Spinach makes you strong. Vegetable Marketing Queensland. Accessed September 10, 2020. https:www.fakevegetablemarketing.com.au
