How to cite online articles that don't have a publication date?
The APA blog answers this:

Determining Website Dates
If no date of publication is provided, use the letters n.d. (which stand for “no date”). The copyright date on the website itself should not be used as the publication date for particular content on that site.

(Note that you should use the updated date if there is one.)
When you have multiple citations for the same website and both have no date, you should append a letter to the end, similar to an actual year: “n.d.-a”, “n.d.-b”, etc.