Hi,
Thank you for your interest in Syncfusion products.
1. I am able to see the issue of the date parameter having negative values does not parsed properly. This seems to be an issue, and can you please post an incident so that we can create a bug report and work on it with the incident as reference.
2. The UseDatesInCalculation works as expected just similar to the MS Excel. Please check the sample in the Manual Calculation form to calculate the date with this property enabled.
The sample has been attached in the below location:
http://www.syncfusion.com/uploads/redirect.aspx?&team=support&file=DateCalc1576590819.zipLet me know if you have any queries.
Regards,
Nirmal