diff --git a/.github/workflows/registry-source.yaml b/.github/workflows/registry-source.yaml
index 0fdd3db..d39fe46 100644
--- a/.github/workflows/registry-source.yaml
+++ b/.github/workflows/registry-source.yaml
@@ -23,6 +23,11 @@ on:
         required: false
         type: boolean
         default: false
+      allow_bootstrap:
+        description: 'Onboarding only: permit a single-day rebuild when no asset has ever been published'
+        required: false
+        type: boolean
+        default: false
 
 # Keyed on the source: without it every matrix leg shares one group and the legs cancel
 # each other, which is the opposite of running them in parallel.
@@ -70,8 +75,9 @@ jobs:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
           SOURCE: ${{ inputs.source }}
           RUN_DATE: ${{ inputs.date }}
+          BOOTSTRAP: ${{ inputs.allow_bootstrap && '1' || '' }}
         run: |
-          python "src/create_daily_${SOURCE}_release.py" ${RUN_DATE:+--date "$RUN_DATE"}
+          python "src/create_daily_${SOURCE}_release.py" ${RUN_DATE:+--date "$RUN_DATE"} ${BOOTSTRAP:+--allow-bootstrap}
           # Stage into one directory so every leg's artifact has the same root; a second
           # search path would move the root to the common ancestor for some legs only.
           shopt -s nullglob
@@ -93,4 +99,6 @@ jobs:
           name: registry-${{ inputs.source }}
           path: data/registry-out
           retention-days: 1
-          if-no-files-found: error
+          # A tolerated source that failed has nothing to upload; only a required
+          # source missing its artifact is an error.
+          if-no-files-found: ${{ inputs.required && 'error' || 'ignore' }}
diff --git a/src/create_daily_faa_release.py b/src/create_daily_faa_release.py
index b668518..8e5e49f 100644
--- a/src/create_daily_faa_release.py
+++ b/src/create_daily_faa_release.py
@@ -4,6 +4,10 @@ import argparse
 
 parser = argparse.ArgumentParser(description="Create daily FAA release")
 parser.add_argument("--date", type=str, help="Date to process (YYYY-MM-DD format, default: today)")
+parser.add_argument("--allow-bootstrap", action="store_true",
+                    help="Permit rebuilding from a single day when no published asset is found. "
+                         "Onboarding only: a missing asset is otherwise indistinguishable from a "
+                         "transient outage, and rebuilding would erase the accumulated history.")
 args = parser.parse_args()
 
 if args.date:
@@ -43,7 +47,13 @@ df_new = convert_faa_master_txt_to_df(zip_path, date_str)
 try:
     df_base, start_date_str = get_latest_aircraft_faa_csv_df()
 except FileNotFoundError as e:
-    print(f"No existing FAA release found, bootstrapping from today only: {e}")
+    if not args.allow_bootstrap:
+        raise SystemExit(
+            f"No published FAA asset found: {e}\n"
+            "This is indistinguishable from a transient outage, and rebuilding from one day "
+            "would erase the accumulated history. Pass --allow-bootstrap when onboarding."
+        ) from None
+    print(f"Bootstrapping FAA from today only (--allow-bootstrap): {e}")
     df_base = None
     start_date_str = date_str
 
diff --git a/src/create_daily_tc_release.py b/src/create_daily_tc_release.py
index ecfc508..ba7ae3b 100644
--- a/src/create_daily_tc_release.py
+++ b/src/create_daily_tc_release.py
@@ -4,6 +4,10 @@ import argparse
 
 parser = argparse.ArgumentParser(description="Create daily Transport Canada release")
 parser.add_argument("--date", type=str, help="Date to process (YYYY-MM-DD format, default: today)")
+parser.add_argument("--allow-bootstrap", action="store_true",
+                    help="Permit rebuilding from a single day when no published asset is found. "
+                         "Onboarding only: a missing asset is otherwise indistinguishable from a "
+                         "transient outage, and rebuilding would erase the accumulated history.")
 args = parser.parse_args()
 
 if args.date:
@@ -57,7 +61,13 @@ df_new = convert_tc_ccarcs_to_df(zip_path, date_str)
 try:
     df_base, start_date_str = get_latest_aircraft_tc_csv_df()
 except FileNotFoundError as e:
-    print(f"No existing Transport Canada release found, bootstrapping from today only: {e}")
+    if not args.allow_bootstrap:
+        raise SystemExit(
+            f"No published Transport Canada asset found: {e}\n"
+            "This is indistinguishable from a transient outage, and rebuilding from one day "
+            "would erase the accumulated history. Pass --allow-bootstrap when onboarding."
+        ) from None
+    print(f"Bootstrapping Transport Canada from today only (--allow-bootstrap): {e}")
     df_base = None
     start_date_str = date_str