diff --git a/B09_Estimation/B09_Estimation_Bill_Library.py b/B09_Estimation/B09_Estimation_Bill_Library.py
index 538f200ff..a53d71108 100644
--- a/B09_Estimation/B09_Estimation_Bill_Library.py
+++ b/B09_Estimation/B09_Estimation_Bill_Library.py
@@ -340,24 +340,43 @@ def copies(project_root: str | Path) -> list[tuple[Path, dict[str, Any]]]:
     return out
 
 
-def used_folders(user: dict[str, Any]) -> set[str]:
+def used_folders(user: dict[str, Any], project_root: str | Path | None = None) -> set[str]:
     """설계내역서 덮개 줄 · 거리이정표 운반 연결(251-5)이 잇는 서고 사본 폴더 +
-    일위대가 복사본(703-2 `@copy`)의 원본 사본."""
-    copies = [
-        str(lines["@copy"].get("from") or "")
-        for lines in (user.get("daega_cover") or {}).values()
+    일위대가 복사본(703-2 `@copy`)의 원본 사본 — 복사본의 복사본(`K:`)은 맨 처음 원본까지 ·
+    사전조합 원본(`C:참조`) = 그 참조를 담은 사본 폴더(`project_root` 줄 때)."""
+    covers = user.get("daega_cover") or {}
+
+    def origin(src: str) -> str:
+        seen: set[str] = set()
+        while src.startswith("K:") and src not in seen:
+            seen.add(src)
+            src = str(((covers.get(src) or {}).get("@copy") or {}).get("from") or "")
+        return src
+
+    srcs = {
+        origin(str(lines["@copy"].get("from") or ""))
+        for lines in covers.values()
         if isinstance(lines, dict) and isinstance(lines.get("@copy"), dict)
-    ]
-    return {
-        str(ref["lib"])
-        for row in ref_rows(user)
-        if isinstance(ref := row.get("ref"), dict) and ref.get("tab") == "dg" and ref.get("lib")
-    } | {src[2:] for src in copies if src.startswith("L:")}
+    }
+    pre = {src[2:] for src in srcs if src.startswith("C:")}
+    return (
+        {
+            str(ref["lib"])
+            for row in ref_rows(user)
+            if isinstance(ref := row.get("ref"), dict) and ref.get("tab") == "dg" and ref.get("lib")
+        }
+        | {src[2:] for src in srcs if src.startswith("L:")}
+        | {
+            folder.name
+            for folder, manifest in (copies(project_root) if pre and project_root else [])
+            if refs.ref_id((manifest.get("원본") or {}).get("참조") or {}) in pre
+        }
+    )
 
 
 def prune(project_root: str | Path, user: dict[str, Any]) -> list[str]:
     """[저장] 뒤 — 줄이 안 잇는 사본 폴더를 지움(다시 고르면 새로 들여옴) · 지운 이름."""
-    keep = used_folders(user)
+    keep = used_folders(user, project_root)
     base = library_dir(project_root)
     gone = []
     for child in sorted(base.iterdir()) if base.is_dir() else []:
diff --git a/B09_Estimation/B09_Estimation_Router.py b/B09_Estimation/B09_Estimation_Router.py
index 2e6424a3a..b414a1727 100644
--- a/B09_Estimation/B09_Estimation_Router.py
+++ b/B09_Estimation/B09_Estimation_Router.py
@@ -210,7 +210,7 @@ async def _demand(root: Path, draft: dict[str, Any] | None = None) -> list[str]:
     """단가 수요 키 — 연결된 사본 + 설계내역서 손 줄 로직(166-2) +
     거리이정표 운반 연결(251-5) · draft = 화면 캐시(296 · 서고 사본 = 그 줄이 잇는 것만)."""
     user = await asyncio.to_thread(calc_user, root, draft)  # 운반 값 사본 먼저(263-2)
-    keep = None if draft is None else library.used_folders(user)
+    keep = None if draft is None else library.used_folders(user, root)
     keys = await asyncio.to_thread(linked_resource_keys, root, keep)
     hand = await asyncio.to_thread(sangeun.hand_resource_keys, user)
     hand = [*hand, *added_keys(user.get("daega_cover"))]  # 705-2 붙인 줄 이음
diff --git a/resources/tester/test_703_b09_daega_copy.py b/resources/tester/test_703_b09_daega_copy.py
index b1f272386..c4930ef5c 100644
--- a/resources/tester/test_703_b09_daega_copy.py
+++ b/resources/tester/test_703_b09_daega_copy.py
@@ -96,6 +96,28 @@ def test_서고_사본_원본_지킴():
     assert library.used_folders(user) == {"combo@system@-@SS1"}
 
 
+def test_사전조합_원본_복사본_사본_지킴(tmp_path):
+    """통합 점검 — 사전조합(`C:참조`) 복사본 · 복사본의 복사본 = 원본 사본 폴더 지킴(업데이트 수요 · 저장 정리)."""
+    base = library.library_dir(tmp_path)
+    for name, ref in (
+        ("precombo@personal@1-3@SC-000001", {"층": "personal", "주인": "1/3", "키": "SC-000001"}),
+        ("precombo@personal@1-3@SC-000002", {"층": "personal", "주인": "1/3", "키": "SC-000002"}),
+    ):
+        (base / name).mkdir(parents=True)
+        manifest = {"종류": "precombo", "원본": {"참조": ref}}
+        (base / name / "manifest.json").write_text(json.dumps(manifest), encoding="utf-8")
+    src = "C:참조|personal|1/3|SC-000001"
+    user = {
+        "daega_cover": {
+            "K:aa": {"@copy": {"from": src, "name": "복사"}},
+            "K:bb": {"@copy": {"from": "K:aa", "name": "복사의 복사"}},
+        }
+    }
+    assert library.used_folders(user) == set()  # 폴더 모름 = 옛 꼴
+    assert library.used_folders(user, tmp_path) == {"precombo@personal@1-3@SC-000001"}
+    assert library.prune(tmp_path, user) == ["precombo@personal@1-3@SC-000002"]
+
+
 # ── 내 자료집(개인 층 사전조합 · 임시 storage) ─────────────────────────────