Ask most people how to make an English noun plural and they'll say "add an s".
Mostly true. But even if you ignore the irregulars (add an N, change the vowel, don't do anything: oxen, feet, deer), that's a great oversimplification of the real rule.
You have to look at the final sound. Then follow this simple :-) flowchart:
(So, mostly you write S and say Z.)
In other words, Davis is made plural by adding -es: Davises.
So, thanks, charity asking for donations and sending us holiday labels. But we won't be using them.