I am trying to systematically display BCE data and I have discovered something strange. When perform a calculate field on a date field and enter a value of -500000 the result is 16/01/531. Zero is 30/12/1899
I didn't think that the time suite worked this way?
The story behind 30-Dec-1899 as the "Zero Date" is a long one, but pretty well summarized here at Stack Overflow.
How is your data being stored? Other databases and programs have similarly long-established and sometimes-interesting stories behind their "Zero Date", like IBM SPSS's October 14, 1582, which never actually existed.