diff --git a/scratch/offset_hist_scan.py b/scratch/offset_hist_scan.py
index 1a2b9a1..a43a097 100644
--- a/scratch/offset_hist_scan.py
+++ b/scratch/offset_hist_scan.py
@@ -62,12 +62,31 @@ _STEM = re.compile(r"^([B-Z])(\d{3})")
 _B36 = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ"
 
 
-def serial_of(name: str) -> str:
-    """`P036L318.C80H` -> `BE14036`.  See CLAUDE.md, serial encoding."""
+_SERIAL_RE = re.compile(rb"\b([A-Z]{2}\d{3,6})\b")
+
+
+def serial_of(name: str, path=None) -> str:
+    """Real serial for a BW file.
+
+    The filename encodes only the NUMBER: `<letter><3 digits>` where
+    letter = chr(ord('B') + serial // 1000).  The two-letter family prefix
+    ("BE", "BA", ...) is **not** in the filename, so it must be read out of
+    the file body.  Four units in the DL2 archive are BA, not BE — assuming
+    "BE" mislabels BA9229, BA10060, BA10895 and BA15957.
+    """
     m = _STEM.match(name)
     if not m:
         return "?"
-    return f"BE{(ord(m.group(1)) - ord('B')) * 1000 + int(m.group(2))}"
+    num = (ord(m.group(1)) - ord("B")) * 1000 + int(m.group(2))
+    if path is not None:
+        try:
+            for s in _SERIAL_RE.findall(Path(path).read_bytes()):
+                s = s.decode()
+                if s[2:].lstrip("0") == str(num):
+                    return s
+        except Exception:
+            pass
+    return f"BE{num}"          # last-resort fallback; prefix unverified
 
 
 def stem_time(name: str):
@@ -141,7 +160,7 @@ def scan(path_str: str):
     for ch, st in stats.items():
         others = [stats[o]["p5"] for o in stats if o != ch]
         rows.append({
-            "serial": serial_of(p.name),
+            "serial": serial_of(p.name, p),
             "timestamp": stamp,
             "filename": p.name,
             "channel": ch,
diff --git a/scratch/offset_scan3.py b/scratch/offset_scan3.py
index 2c2b953..3a3cde6 100644
--- a/scratch/offset_scan3.py
+++ b/scratch/offset_scan3.py
@@ -28,9 +28,31 @@ from minimateplus.event_file_io import read_blastware_file
 GEO=("Tran","Vert","Long"); K=10.0/32000.0
 _WAVE=re.compile(r"\.[A-Za-z0-9]{2}0[Ww]$"); _STEM=re.compile(r"^([B-Z])(\d{3})")
 
-def serial_of(n):
-    m=_STEM.match(n)
-    return f"BE{(ord(m.group(1))-ord('B'))*1000+int(m.group(2))}" if m else "?"
+_SERIAL_RE = re.compile(rb"\b([A-Z]{2}\d{3,6})\b")
+
+
+def serial_of(name: str, path=None) -> str:
+    """Real serial for a BW file.
+
+    The filename encodes only the NUMBER: `<letter><3 digits>` where
+    letter = chr(ord('B') + serial // 1000).  The two-letter family prefix
+    ("BE", "BA", ...) is **not** in the filename, so it must be read out of
+    the file body.  Four units in the DL2 archive are BA, not BE — assuming
+    "BE" mislabels BA9229, BA10060, BA10895 and BA15957.
+    """
+    m = _STEM.match(name)
+    if not m:
+        return "?"
+    num = (ord(m.group(1)) - ord("B")) * 1000 + int(m.group(2))
+    if path is not None:
+        try:
+            for s in _SERIAL_RE.findall(Path(path).read_bytes()):
+                s = s.decode()
+                if s[2:].lstrip("0") == str(num):
+                    return s
+        except Exception:
+            pass
+    return f"BE{num}"          # last-resort fallback; prefix unverified
 
 def scan(ps):
     p=Path(ps)
@@ -48,7 +70,7 @@ def scan(ps):
             mid, end = a[t:2*t], a[2*t:]
             if not pre or not mid or not end: continue
             v=[statistics.median(x)*K for x in (pre,mid,end)]
-            out.append({"serial":serial_of(p.name),"timestamp":stamp,
+            out.append({"serial":serial_of(p.name, p),"timestamp":stamp,
                         "filename":p.name,"channel":ch,
                         "pretrig_n": pre_n or 0,
                         "pre":round(v[0],4),"mid":round(v[1],4),"end":round(v[2],4),