Hello @kwilz ,
Since your model has input variables, forecasting of the response variable needs values on these input variables. The warning messages indicate that your input data set does not contain the values for these input variables for the future periods when you wanted to obtain forecasts, hence forecast into the future periods cannot be obtained. The following section of PROC ARIMA documentation discusses this when forecasting with input variables:
https://go.documentation.sas.com/doc/en/pgmsascdc/v_032/etsug/etsug_arima_gettingstarted40.htm
Because your input variables are AO dummy variables, you know their future values, so you can simply add values for these inputs in your data set for the length of future periods when you want to compute forecast, and set response variable to missing, then forecasts for these future periods will be computed.
I hope this helps.
... View more