diff --git a/tunie/research/reference-maps/compose_arrow_delete.py b/tunie/research/reference-maps/compose_arrow_delete.py
index 8a6eee8..eaabc8d 100644
--- a/tunie/research/reference-maps/compose_arrow_delete.py
+++ b/tunie/research/reference-maps/compose_arrow_delete.py
@@ -38,6 +38,7 @@ from __future__ import annotations
 
 import sys
 
+import checksum
 from decode_map import decode, encode
 from toggle_devices import SAI, O2_1, O2_2, repack, unpack
 
@@ -77,6 +78,11 @@ def compose(arrow_raw: bytes, stock_after_raw: bytes, delete_raw: bytes) -> tupl
             f"  (byte {before} -> {after})"
         )
 
+    before_sum = checksum.stored(bytes(arrow_rom))
+    checksum.patch(arrow_rom)
+    after_sum = checksum.compute(bytes(arrow_rom))
+    notes.append(f"checksum: stored {before_sum:04x} (stale) -> patched {after_sum:04x}")
+
     repacked = repack(arrow_dec, bytes(arrow_rom), positions)
     out = encode(repacked)
     assert decode(out) == repacked, "round-trip failed"
@@ -101,8 +107,9 @@ def main() -> int:
     for n in notes:
         print(" ", n)
     print(f"wrote {out_path} ({len(out)} bytes)")
-    print("NOTE: flash checksum not patched -- not known to be flashable as-is.")
     print("NOTE: main VE fuel-table overlap (~1340 bytes) still unresolved -- see COMMUNITY_TUNING.md.")
+    print("NOTE: only device flags + 2 idle-CO trim bytes are composed -- the main")
+    print("      running-range VE fuel tables are untouched stock-Arrow calibration.")
     return 0
 
 
diff --git a/tunie/research/reference-maps/derived/20262-arrow-delete-composed.hex b/tunie/research/reference-maps/derived/20262-arrow-delete-composed.hex
index 2fcb37d..3574ce8 100644
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diff --git a/tunie/research/reference-maps/derived/20313-arrow-delete-composed.hex b/tunie/research/reference-maps/derived/20313-arrow-delete-composed.hex
index ab32fde..45caa70 100644
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