I went through Vana, Virata and Udyoga Parvas. Tired and exhausted. But was worth the effort. Now I have to do the write up for my findings.
The conclusion is that Pandavas completed 13 years by Solar calendar/year calculations.
Useful byproducts of this investigation led to:
(1) time of the beginning of Pandava’s exile (+/-1 month)
(2) The Date of Uttara-Abhimanyu wedding could be estimated to be a period of 17 days (wedding occurred during this 17 day period)
(3) The Date when Purohit of King Drupada leaving for Hastinapur could be estimated.
(4) The Date of Kichaka Vadha could be estimated and also timings – when Arjuna came into the open and when all 5 Pandavas came out in the open from their Ajnatvas.