Integrating national compensation survey data with DIY local survey data

My agency conducted its own salary survey to capture local and state data for the same and related industries. I have already calculated its results with survey sample means for each position, with t-distribution margins of error for the population means at 95% confidence. How can I reliably supplement or combine small sample size survey data with national-level , industry-specific survey data?

If I compared the sample position means from each survey, weighted (or unweighted) accordingly, could I use “means of the means” (with confidence levels) as reliable market-level salaries? Is there any way to predict whether this method would produce reliable data (other than trying both to see what happens)?

Thanks.