Numbers changing fields to "0"
Hello! OS 10.14.6:
I have a basic spreadsheet in Numbers that I am using for securities trading records, with various dates, words and dollar amounts in different fields. However, when I enter an assortment of dates, such as "12/19,21,22", as soon as I leave the field, Numbers changes it to just a "0." This is incredibly frustrating. (Only way around it is to add the word "or" or "and" between any of the numbers, but that takes up more room/time than necessary.)
What am I doing wrong and/or how can I get around this?
Thanks very much, community!
iMac, OS X 10.10