Customer AI historical data requirement

In customer AI historical data requirements, its mentioned that data required = Eligible lookback window + outcome window. Where the eligible lookback window is defined in the eligible population. 

So, if I set eligible population to be something like - web activity in last 60 days and set goal condition to happen in upcoming 30 days, total data required would be 60 + 30 = 90 days. As per my understanding, it means the model would train on last 90 days of historical data. Then, I think model will look beyond "web activity in last 60 days. I fail to understand, how is eligible population working if model requires 90 days of historical data?

Also, is lookback window/eligible population limited to 120 days?

(image is taken from adobe documentation - https://experienceleague.adobe.com/en/docs/experience-platform/intelligent-services/customer-ai/data-requirements )