diff --git a/prereise/gather/griddata/hifld/data_process/generators.py b/prereise/gather/griddata/hifld/data_process/generators.py
index aab368c5a..44b84007a 100644
--- a/prereise/gather/griddata/hifld/data_process/generators.py
+++ b/prereise/gather/griddata/hifld/data_process/generators.py
@@ -126,8 +126,10 @@ def estimate_heat_rate_from_ampd(generators, epa_ampd):
 
 
 def add_heat_rate_to_generators(generators, ampd_heat_rates, epa_needs):
-    # Heat rates come from epa_needs data frame
-    # Mapping by plant code or plant name seems to have
+    # In the collaborators' implementation, AMPD heat rates were used when possible,
+    #   otherwise using only the linear heat-rate component from NEEDS.
+    # Mapping by generators unit name to NEEDS name and mapping plant code both have
+    #   about 78% success rate.
     pass