When we update the Start/Finish Date of the project via XOG, it seems we are not able to specify later than 03/Jun/2079. If we specify the date value later than the date, we get the following error and the XOG IN fails.
<Description>[Error] :0:0: attribute "budgetCostFinish" has a bad value: the value is out of the range (maxExclusive specifies 2079-6-3T0:0:0.000).
Invalid attribute in input document. Please remove all instances of attribute from document elements and try again.
[Element : Project, Attribute : budgetCostFinish ].
It is working by design.
According to our test, it looks we can specify the date later than 03/Jun/2079 to a custom attribute on out-of-the-box or a custom Object, but we do not recommend specifying the date later than the maximum value because in most areas of the application, 2079 is set as the limitation and also we do not recommend to track projects beyond 10 years due to a performance issue.