I use the forecast tab extensively in combination with split revenue between sales reps. Forecast shows this quickly and easily however I look at previous years data for comparison and the forecast tab only allows me to go back 12 months. How can expand the look back 18, 24+ months?
Salesforce Forecast tab doesn't go beyond 12 months.
You can prepare reports on Forecasting. Refer Create a Custom Report Type in Collaborative Forecasts
For this create new Report Type, selecting
Forecasting Items or
Forecasting Quotas and related child objects like
In the report you could specify wide range of forecasting tenure.