The date of publication is required for all end references.
If no year of publication is available, use the year of copyright. When citing online sources that have a “last modified” date, use that date in addition to or instead of a date of publication. If there is no date for an online source, use the access date instead.
From CSE Manual 9th ed., Ch. 29.3.3.6 Date
Copyright date:
c2020.
No date:
al-Khwārizmī MM. Al-Kitāb al-mukhtaṣar fī ḥisāb al-jabr waʾl-muqābala [The compendious book on calculation by completion and balancing]. [date unknown]. or . . . [9th century].