I read over the explanation of the IV strategy to try to capture whether appointment of a business manager was endogenous (we need to cut costs) or exogenous (t

I read over the explanation of the IV strategy to try to capture whether appointment of a business manager was endogenous (we need to cut costs) or exogenous (the predecessor died or retired). I think there's still something missing. Business managers seem to be more common in older businesses that have saturated their market share. If my observation is true it would confound the finding that revenue does not increase when a business manager is appointed. They may be more likely to be appointed to a role where revenue cannot be increased. Maybe the authors could use a factor like company age normalized by the median tenure of a company in the S&P 500 at that time to identify younger, more dynamic companies?