here is an example where multiple sessions were done in different scanners, but top level .json has one of them listed (should have none)
$ grep DeviceSerialNumber task-efnback_bold.json sub-000001/ses-01/func/sub-000001_ses-01_task-efnback_run-01_bold.json sub-000001/ses-02/func/sub-000001_ses-02_task-efnback_run-01_bold.json
task-efnback_bold.json: "DeviceSerialNumber": "35216",
sub-000001/ses-01/func/sub-000001_ses-01_task-efnback_run-01_bold.json: "DeviceSerialNumber": "35216",
sub-000001/ses-02/func/sub-000001_ses-02_task-efnback_run-01_bold.json: "DeviceSerialNumber": "67078",
here is an example where multiple sessions were done in different scanners, but top level .json has one of them listed (should have none)