diff --git a/src/mjolnir/graphenhancer.cc b/src/mjolnir/graphenhancer.cc
index e310e1d70d..97070dd6a7 100644
--- a/src/mjolnir/graphenhancer.cc
+++ b/src/mjolnir/graphenhancer.cc
@@ -1668,6 +1668,9 @@ void enhance(const boost::property_tree::ptree& pt,
         // Check for not_thru edge (only on low importance edges). Exclude
         // transit edges
         if (directededge.classification() > RoadClass::kTertiary) {
+          // (nils): if we want to update all edges in a not_thru region, we'd have to
+          // go through more tiles than just this one.. we could record the entire set of
+          // not_thru edges for all tiles and rip through them again after this big loop?
           if (IsNotThruEdge(reader, lock, startnode, directededge)) {
             directededge.set_not_thru(true);
             stats.not_thru++;
diff --git a/src/thor/bidirectional_astar.cc b/src/thor/bidirectional_astar.cc
index 99ea3417b6..efd559e73d 100644
--- a/src/thor/bidirectional_astar.cc
+++ b/src/thor/bidirectional_astar.cc
@@ -319,6 +319,10 @@ inline bool BidirectionalAStar::ExpandInner(baldr::GraphReader& graphreader,
                           : astarheuristic_reverse_.Get(t2->get_node_ll(meta.edge->endnode()), dist));
 
   // not_thru_pruning_ is only set to false on the 2nd pass in route_action.
+  // NOTE(nils): not_thru_pruning() will be false for the correlated (i.e. "first") edges as pred. if
+  // the current edge is also not_thru we won't prune in the next round. if the current edge is not a
+  // not_thru we will start pruning next round. that ensures that we can start on a not_thru edge and
+  // continue on other not_thru edges before pruning.
   bool thru = not_thru_pruning_ ? (pred.not_thru_pruning() || !meta.edge->not_thru()) : false;
 
   // Add edge label, add to the adjacency list and set edge status
@@ -604,6 +608,10 @@ BidirectionalAStar::GetBestPath(valhalla::Location& origin,
         // on later, causing us to needlessly expand when we could have aborted sooner. However, it
         // ensures that most impossible route will fail fast provided one of the locations didn't
         // start from a not_thru/closed edge
+        // TODO(nils):
+        //   1. extended_search doesn't seem to do what it's documented to do; it will force both
+        //      both directions to be eventually exhausted, no matter if the other direction
+        //      started on a closure/not_thru
         if (!extended_search_ || !pruning_disabled_at_destination_) {
           return {};
         }
diff --git a/src/thor/costmatrix.cc b/src/thor/costmatrix.cc
index 134eaace52..4f53e6c2cf 100644
--- a/src/thor/costmatrix.cc
+++ b/src/thor/costmatrix.cc
@@ -567,6 +567,11 @@ void CostMatrix::BackwardSearch(const uint32_t index, GraphReader& graphreader)
   edgestate.Update(pred.edgeid(), EdgeSet::kPermanent);
 
   // Prune path if predecessor is not a through edge
+  // NOTE(nils): this will also be forward-compatible
+  // this is currently a problem when edges in not_thru
+  // areas are not marked, as expansion will just stop in this direction
+  // and continue in the other direction even though it wouldn't be able to
+  // find this tree inside the not_thru region
   if (pred.not_thru() && pred.not_thru_pruning()) {
     return;
   }
@@ -777,6 +782,8 @@ void CostMatrix::SetSources(GraphReader& graphreader,
 
       // Set the initial not_thru flag to false. There is an issue with not_thru
       // flags on small loops. Set this to false here to override this for now.
+      // NOTE(nils): shouldn't not_thru_pruning be set to the opposite of the edge's not_thru flag?
+      // current code should also be compatible with new data
       BDEdgeLabel edge_label(kInvalidLabel, edgeid, oppedge, directededge, cost, mode_, ec, d, false,
                              true, static_cast<bool>(flow_sources & kDefaultFlowMask),
                              InternalTurn::kNoTurn, -1);