Found 4!
🚂 Westbound
Green-D train #3909-3914
incoming at Government Center Station - Green Line Westbound
🚂 Eastbound
Green-D train #3921-3901
incoming at Waban Station - Inbound
🚂 Eastbound
Green-B train #3919-3922
stopped at Packards Corner - Inbound
🚂 Westbound
Green-C train #3907-3916
stopped at Boylston Station - Outbound