Found 4!
🚂 Westbound
Green-D train #3909-3906
in transit to Chestnut Hill Station - Outbound
🚂 Westbound
Green-C train #3907-3910
incoming at Kent St - Outbound
🚂 Eastbound
Green-B train #3923
incoming at Arlington Station - Inbound
🚂 Westbound
Green-B train #3921-3901
stopped at Chestnut Hill Ave - Outbound