Shri Phadnis writes….
“We have yet to hear from Shri. Oak, what, according to him, was the system of taking adhika masas in mahabharat times, where it is stated in mahabharat or contemporary texts and whether it was accurate.”
What we know (as of now) for the system of Adhika masa in Mahabharata times is contained in the following shloka(s).
(1) विराट पर्व (CE ४७:३-४, GP ५२:३-४)
तेषां कालातिरेकेण ज्योतिषां च व्यतिक्रमात
पंचमे पंचमे वर्षे द्वौ मासावुपजायत:
तेषामभ्यधिका मासा: पंच द्वादश च क्षपा:
त्रयोदशानां वर्षाणामिती मे वर्तते मति:
(2) विराट पर्व (Bombay edition ४७:३)
गते वर्षद्वये चैव पंचपक्षे दिनद्वये
दिवसाष्टमे भागे पतत्येकोधिकमास:
We do not have any additional insights and we should not claim more than what can be ascertained.
What we can indeed ascertain, assuming our understanding and rationale for synchronizing Luni-solar calendar in our times to be same as that of Mahabharata times, is that system of inserting ‘2 consecutive months’ at the end of 58 months (all lunar) would simply not work. It would not work now and it would not have worked then.