Okay. I did dig in a little. It looks like at least some of the vehicles missing data are waiting to begin a trip. Here's one that's at Harvard waiting to start a trip to Nubian. Is it possible to default vehicles to MANY_SEATS_AVAILABLE before they've started a trip?
{
"attributes": {
"bearing": 315,
"current_status": "IN_TRANSIT_TO",
"current_stop_sequence": 1,
"direction_id": 0,
"label": "1857",
"last_updated": "2020-06-29T15:47:18-04:00",
"latitude": 42.37274,
"longitude": -71.11651,
"occupancy_status": null,
"speed": null,
"updated_at": "2020-06-29T15:47:18-04:00"
},
"id": "y1857",
"links": {
"self": "/vehicles/y1857"
},
"relationships": {
"route": {
"data": {
"id": "1",
"type": "route"
}
},
"stop": {
"data": {
"id": "110",
"type": "stop"
}
},
"trip": {
"data": {
"id": "45030930",
"type": "trip"
}
}
},
"type": "vehicle"
},