Solar Vs Lunar Calender

Vaisampayana said, 'King Duryodhana then, on the field of battle said unto Bhishma, and unto Drona--that tiger among warriors, and unto Kripa--that mighty car-warrior, these words, 'Both myself and Kama had said this unto the preceptors 1 I refer to the subject again, for I am not satisfied with having said it once. Even this was the pledge of the sons of Pandu that if defeated (at dice) they would reside to our knowledge in countries and woods for twelve years, and one more year unknown to us. That thirteenth year, instead of being over, is yet running. Vibhatsu, therefore, who is still to live undiscovered hath appeared before us. And if Vibhatsu hath come before the term of exile is at end, the Pandavas shall have to pass another twelve years in the woods. Whether it is due to forgetfulness (on their part) induced by desire of dominion, or whether it is a mistake of ours, it behoveth

Bhishma to calculate the shortness or excess (of the promised period). When an object of desire may or may not be attained, a doubt necessarily attaches to one of the alternatives, and what is decided in one way often ends differently. 

Meaning

1. According to Solar Calender the Time of Exile of Pandavas was Not Over 
2. According to Lunar Calender the Time of Exile of Pandavas was Over

Source

1. http://s01m.blogspot.com/2013/12/calendars.html
2. http://k00y.blogspot.com/2013/12/sun-vs-moon.html