The 14-day default retention refers to any of the data in EUM that is stored in the Events Service. That is typically data you are seeing under BRUM and MRUM sessions. (all the raw event data)
To clarify, any aggregated metric that you see in EUM would still have the standard 13-month retention.
The data in Events Service typically just gets overwritten after the retention timeframe.
You could potentially purchase a longer retention policy. We do have some customers who purchase 30-day or even 60-day events data retention. For purchasing longer retention data, please contact your AppD Rep.