I need academic quotes (e.g. journals, textbooks, etc.) from
statistics on a rule of thumb about how many periods into the future
can be reasonably forecasted from using x number of historical
periods. For example, if someone uses 2 years of historical revenue
data, how many years into the future can they reasonalbe forecast?
1yr? 5yrs? 25yrs???

We have 2 years of historical data (annual not monthly) on revenue and
number of new customers. From this data, someone predicted long-term
future revenues and new customers for 25 years into the future. I want
to show this is rediculous. I need strong academic quotes showing that
statistically
speaking it is ridiculous to predict 25 years into the future from
only 2 years of historical data.