2 issues with TIMESTAMPDIFF:
1.

select TIMESTAMPDIFF(SQL_TSI_DAY,parseDate('2012-01-01', 'yyyy-MM-dd'),parseDate('2304-04-12', 'yyyy-MM-dd'));

result = 106751

If you increase the end date by 1 day:

select TIMESTAMPDIFF(SQL_TSI_DAY,parseDate('2012-01-01', 'yyyy-MM-dd'),parseDate('2304-04-13', 'yyyy-MM-dd'))

result = -106751. I would expected the answer to be 106752

2. Both MS Excel and Oracle give the number of days between 1-Jan-2012 and 12-Apr-2304 as 106752, not the 106751 that EDS is reporting.