The respective State Shops Act provides for a maximum permissible PL accumulation, which in most cases is 2 years of leave. Hence, depending on the state you are in, 42 days may be the right limit, over and above which the leaves may lapse as per company policy. Actually, your company should not have shown 70 days of PL to your credit in the first place, which is causing this confusion. They should have lapsed any leaves beyond 42 days. In my existing company, we also have a limit of 42 PL days, which can be encashed at the time of exit.
Regards