diff --git a/core/release_config.mk b/core/release_config.mk
index 36882bb..a7b5b3f 100644
--- a/core/release_config.mk
+++ b/core/release_config.mk
@@ -133,6 +133,18 @@
 )
 FLAG_DECLARATION_FILES :=
 
+# Verify that all inherited/overridden release configs are declared.
+$(foreach config,$(_all_release_configs),\
+  $(foreach r,$(all_release_configs.$(r).OVERRIDES),\
+    $(if $(strip $(_all_release_configs.$(r).FILES)$(_all_release_configs.$(r).OVERRIDES)),,\
+    $(error Release config $(config) [declared in: $(_all_release_configs.$(r).DECLARED_IN)] inherits from non-existent $(r).)\
+)))
+# Verify that alias configs do not have config files.
+$(foreach r,$(_all_release_configs),\
+  $(if $(_all_release_configs.$(r).ALIAS),$(if $(_all_release_configs.$(r).FILES),\
+    $(error Alias release config "$(r)" may not specify release config files $(_all_release_configs.$(r).FILES))\
+)))
+
 ifeq ($(TARGET_RELEASE),)
     # We allow some internal paths to explicitly set TARGET_RELEASE to the
     # empty string.  For the most part, 'make' treats unset and empty string as
@@ -148,8 +160,12 @@
     TARGET_RELEASE = trunk_staging
 endif
 
-ifeq ($(filter $(_all_release_configs), $(TARGET_RELEASE)),)
-    $(error No release config found for TARGET_RELEASE: $(TARGET_RELEASE). Available releases are: $(_all_release_configs))
+# During pass 1 of product config, using a non-existent release config is not an error.
+# We can safely assume that we are doing pass 1 if DUMP_MANY_VARS=="PRODUCT_RELEASE_CONFIG_MAPS".
+ifneq (PRODUCT_RELEASE_CONFIG_MAPS,$(DUMP_MANY_VARS))
+    ifeq ($(filter $(_all_release_configs), $(TARGET_RELEASE)),)
+        $(error No release config found for TARGET_RELEASE: $(TARGET_RELEASE). Available releases are: $(_all_release_configs))
+    endif
 endif
 
 # Choose flag files
@@ -177,7 +193,7 @@
 define declare-release-config
 $(error declare-release-config can only be called from inside release_config_map.mk files)
 endef
-define apply-release-config-overrides
+define _apply-release-config-overrides
 $(error invalid use of apply-release-config-overrides)
 endef
 
@@ -192,12 +208,6 @@
 endif
 .KATI_READONLY := TARGET_RELEASE
 
-# Verify that alias configs do not have config files.
-$(foreach r,$(_all_release_configs),\
-  $(if $(_all_release_configs.$(r).ALIAS),$(if $(_all_release_configs.$(r).FILES),\
-    $(error Alias release config "$(r)" may not specify release config files $(_all_release_configs.$(r).FILES))\
-)))
-
 $(foreach config, $(_all_release_configs), \
     $(eval _all_release_configs.$(config).DECLARED_IN:= ) \
     $(eval _all_release_configs.$(config).FILES:= ) \
diff --git a/core/release_config.scl b/core/release_config.scl
index 629e223..728fc1b 100644
--- a/core/release_config.scl
+++ b/core/release_config.scl
@@ -53,6 +53,7 @@
                     for t in _valid_types
                 ],
             },
+            "origin": {"type": "string"},
             "declared_in": {"type": "string"},
         },
         "optional_keys": {
@@ -80,13 +81,14 @@
     },
 }
 
-def flag(name, partitions, default, *, appends = False):
+def flag(name, partitions, default, *, origin = "Unknown", appends = False):
     """Declare a flag.
 
     Args:
       name: name of the flag
       partitions: the partitions where this should be recorded.
       default: the default value of the flag.
+      origin: The origin of this flag.
       appends: Whether new values should be append (not replace) the old.
 
     Returns:
@@ -112,6 +114,7 @@
         "partitions": partitions,
         "default": default,
         "appends": appends,
+        "origin": origin,
     }
 
 def value(name, value):
@@ -158,7 +161,10 @@
     for key in "name", "partitions", "default", "appends":
         if flag[key] != other[key]:
             return False
-    return True
+    # For now, allow Unknown to match any other origin.
+    if flag["origin"] == "Unknown" or other["origin"] == "Unknown":
+        return True
+    return flag["origin"] == other["origin"]
 
 def release_config(all_flags, all_values):
     """Return the make variables that should be set for this release config.
@@ -234,5 +240,6 @@
         result["_ALL_RELEASE_FLAGS." + flag["name"] + ".VALUE"] = val
         result["_ALL_RELEASE_FLAGS." + flag["name"] + ".DECLARED_IN"] = flag["declared_in"]
         result["_ALL_RELEASE_FLAGS." + flag["name"] + ".SET_IN"] = set_in
+        result["_ALL_RELEASE_FLAGS." + flag["name"] + ".ORIGIN"] = flag["origin"]
 
     return result
diff --git a/tools/releasetools/build_image.py b/tools/releasetools/build_image.py
index a7b1d8c..464ad9b 100755
--- a/tools/releasetools/build_image.py
+++ b/tools/releasetools/build_image.py
@@ -294,7 +294,7 @@
     build_command = [prop_dict["ext_mkuserimg"]]
     if "extfs_sparse_flag" in prop_dict and not disable_sparse:
       build_command.append(prop_dict["extfs_sparse_flag"])
-      run_e2fsck = RunE2fsck
+      run_fsck = RunE2fsck
     build_command.extend([in_dir, out_file, fs_type,
                           prop_dict["mount_point"]])
     build_command.append(prop_dict["image_size"])