The monthly data from 1980M1 to 1990M12(the number of samples is 132). When estimating the model, The using observations of ARIMA(1,1,1) : 1980M3 to 1990M12. (number:130) The using observations of ARIMA(2,1,0):1980M4 to 1990M12. (number:129) The using observations of ARIMA(1,1,0)(1,1,0)12:1983M3 to 1990M12. (number:106) The number of samples is 132. But the number of the using observations depends on order of AR and MA(also SAR and SMA). How can I make them the same for comparing AIC and BIC ?