diff --git a/index.js b/index.js
index 0a8a394..5daf8e4 100644
--- a/index.js
+++ b/index.js
@@ -220,6 +220,7 @@ LANGUAGE sql;
 	// https://github.com/google/transit/blame/217e9bf/gtfs/spec/en/reference.md#L544-L554
 	// However, because we have to use left join instead of an inner join in tables referencing `agency`, this prevents the PostgreSQL query planner from doing some filter pushdowns, e.g.
 	// - when querying `arrivals_departures` by route, stop, date and t_departure/t_arrival
+	// todo: add tests: 0 agencies (implicit single agency), 1 agency
 	{
 		let agencies = 0
 		for await (const agency of await readCsv('agency')) {
diff --git a/lib/stop_times.js b/lib/stop_times.js
index a2ad1c9..ba49db2 100644
--- a/lib/stop_times.js
+++ b/lib/stop_times.js
@@ -225,6 +225,7 @@ WITH stop_times_based AS NOT MATERIALIZED (
 		LEFT JOIN "${opt.schema}".stops stations ON stops.parent_station = stations.stop_id
 		JOIN "${opt.schema}".trips ON s.trip_id = trips.trip_id
 		JOIN "${opt.schema}".routes ON trips.route_id = routes.route_id
+		-- todo: what if the route is missing (LEFT JOIN), does this work?
 		JOIN "${opt.schema}".agency ON routes.agency_id = agency.agency_id
 		JOIN "${opt.schema}".service_days ON trips.service_id = service_days.service_id
 	)
@@ -458,6 +459,7 @@ WITH stop_times_based AS NOT MATERIALIZED (
 			) AS to_wheelchair_boarding
 		FROM "${opt.schema}".trips
 		LEFT JOIN "${opt.schema}".routes ON trips.route_id = routes.route_id
+		-- todo: what if the route is missing (LEFT JOIN), does this work?
 		JOIN "${opt.schema}".agency ON routes.agency_id = agency.agency_id
 		LEFT JOIN "${opt.schema}".stop_times ON trips.trip_id = stop_times.trip_id
 		LEFT JOIN "${opt.schema}".stops from_stops ON stop_times.stop_id = from_stops.stop_id