How much history Google Analytics keeps

Google Analytics keeps the history of individual visitors for a limited time — two months unless someone changes it. Ordinary reports are not affected, but anything that follows the same people over time needs more: customers grouped by the month they arrived, and what a customer is worth.

Glancely needs 14 months, and says so on the property in Settings → Data sources when it has less.

To change it, open Google Analytics → Admin → Data collection and modification → Data retention (in older layouts, Data settings → Data retention), and set both event and user data retention.

Change it early. The setting is not backdated: history builds up from the day you change it.