This is a question more out of curiosity than need to solve a problem, but I'm not sure where else to find the answer, so I turn to this group of expert uses.
I know that FileMaker Pro stores dates as pure numbers, beginning at some point in the past, which I'll call D1 for "Day 1". I'm also pretty sure that D1 is not January 1 of the year 1 CE. But I've heard several different dates mentioned as to what D1 really is, and it's apparently different from one context to another. (Your operating system or Excel, for instance, may use a different D1 than FileMaker does.) What does FileMaker use as its D1?
And, if we want to refer to dates earlier than that (say for a database of historical records or genealogies), does FileMaker compute them (and then presumably store them) as negative numbers?
Getasdate ( 1 ) returns 1/1/0001 So the integer form of a FileMaker date can be defined as the number of days since 12/31/0000
values less than 1 produce evaluation errors and note that "AD" or "BC" type designations are not possible. Therefore FileMaker's date data type does not support dates earlier than this arbitrary value. I'm not an expert on the history of calendars, but you'll have issues with these dates long before you get to "day 1" as the calendar we use today did not exist back then and underwent significant adjustments more than once if I recall what I read correctly.