I was constantly surprsied in my first few games when certain events didn't gain era score. Off the top of my head, things that should trigger era score are:
First city capture
First city capture of a specific opponent
Alliances with an AI for the first time
First joint war
First themed museum
Discovering a natural wonder (not first)
Building 5 unique units, 5 unique improvements, or 3 unique districts (why only the first?)
Manhattan Project
Each stage of the Mars project should be worth 3
Maxing out a promotion tree
Reaching a certain GPT, BPT, CPT threshold (expires after a given era)
Building a national park
World's first spy
Training your first spy
Capturing an enemy spy
Increase the thresholds if necessary to accommodate additions like those.
First city capture
First city capture of a specific opponent
Alliances with an AI for the first time
First joint war
First themed museum
Discovering a natural wonder (not first)
Building 5 unique units, 5 unique improvements, or 3 unique districts (why only the first?)
Manhattan Project
Each stage of the Mars project should be worth 3
Maxing out a promotion tree
Reaching a certain GPT, BPT, CPT threshold (expires after a given era)
Building a national park
World's first spy
Training your first spy
Capturing an enemy spy
Increase the thresholds if necessary to accommodate additions like those.