setting the sample to make a model "solvable"

[jbonanca]

Does anyone know if there is a simple way to set a sample so that a model becomes solvable without generating a "missing data" error message? I am looking to do this for scenarios of models in which some variables are overridden, and it's not obvious to me that there is a simple way of defining the sample so that there are valid values for all exogenous variables at the appropriate lags.

I thought I had found an approach by using "makegroup," but it doesn't cut it -- I don't get a group of the actual series (whether it be a lag specification or an override series) that will be used to generate the solution.

Thank you