diff --git a/scripts/common.py b/scripts/common.py
index a9a2484e..0cc1805a 100644
--- a/scripts/common.py
+++ b/scripts/common.py
@@ -487,6 +487,21 @@ def canonical_target_name(
     return found.pop() if len(found) == 1 else target
 
 
+def truth_target_dir(
+    output_dir: str, platforms: list[str], target: str, platforms_dir: str = "platforms"
+) -> str:
+    """Where a target-narrowed truth model is written and read.
+
+    Slugged from the name the target is filed under: `nx`, `switch` and
+    `nintendo-switch` wrote three copies of one model, and a run under one
+    alias left the others stale beside it. generate_truth writes here and
+    the pipeline's diff reads here, so both call this.
+    """
+    named = canonical_target_name(platforms, target, platforms_dir)
+    slug = re.sub(r"[^a-z0-9]+", "-", named.strip().lower()).strip("-")
+    return os.path.join(output_dir, slug or "target")
+
+
 def load_target_config(
     platform_name: str,
     target: str,
diff --git a/scripts/generate_truth.py b/scripts/generate_truth.py
index 5ce44b76..5d33bbfe 100644
--- a/scripts/generate_truth.py
+++ b/scripts/generate_truth.py
@@ -10,7 +10,6 @@ from __future__ import annotations
 
 import argparse
 import os
-import re
 import sys
 
 sys.path.insert(0, os.path.dirname(__file__))
@@ -21,6 +20,7 @@ from common import (
     load_platform_config,
     load_target_config,
     require_yaml,
+    truth_target_dir,
     write_text_atomic,
     yaml_load,
 )
@@ -94,8 +94,9 @@ def main(argv: list[str] | None = None) -> None:
     # compared a narrowed model against the whole scrape.
     output_dir = args.output_dir
     if args.target:
-        slug = re.sub(r"[^a-z0-9]+", "-", args.target.strip().lower()).strip("-")
-        output_dir = os.path.join(output_dir, slug or "target")
+        output_dir = truth_target_dir(
+            output_dir, platforms, args.target, args.platforms_dir
+        )
     os.makedirs(output_dir, exist_ok=True)
 
     for name in platforms:
diff --git a/scripts/pipeline.py b/scripts/pipeline.py
index fd1c469c..88b06cf7 100644
--- a/scripts/pipeline.py
+++ b/scripts/pipeline.py
@@ -41,7 +41,13 @@ if sys.version_info < (3, 12):
     sys.exit(f"pipeline.py needs Python 3.12 or newer, this is {sys.version.split()[0]}")
 
 sys.path.insert(0, str(Path(__file__).parent))
-from common import ArtifactLockBusy, artifact_lock, hold_artifact_lock
+from common import (
+    ArtifactLockBusy,
+    artifact_lock,
+    hold_artifact_lock,
+    list_registered_platforms,
+    truth_target_dir,
+)
 
 
 def run(cmd: list[str], label: str) -> tuple[bool, str]:
@@ -253,9 +259,12 @@ def _truth_steps(args: argparse.Namespace, results: dict) -> bool:
     # the whole scrape.
     truth_dir = Path(args.output_dir) / "truth"
     if args.target:
-        truth_dir = truth_dir / re.sub(
-            r"[^a-z0-9]+", "-", args.target.strip().lower()
-        ).strip("-")
+        # generate_truth --all writes every registered platform's model.
+        truth_dir = Path(truth_target_dir(
+            str(truth_dir),
+            list_registered_platforms("platforms", include_archived=True),
+            args.target,
+        ))
 
     if args.with_truth or args.with_export:
         truth_cmd = [
diff --git a/tests/test_target_names.py b/tests/test_target_names.py
index fee198ea..d916c08f 100644
--- a/tests/test_target_names.py
+++ b/tests/test_target_names.py
@@ -107,6 +107,31 @@ class EachPlatformNamesTheTargetItsOwnWay(unittest.TestCase):
         self.assertNotIn("args.target = canonical_target_name(", source)
 
 
+class OneTruthModelPerTarget(unittest.TestCase):
+    """generate_truth slugged the typed name: --target nx, switch and
+    nintendo-switch wrote three copies of one model, and the pipeline's diff
+    rebuilt the same slug by hand to find it."""
+
+    def test_aliases_share_a_directory(self):
+        from common import list_registered_platforms, truth_target_dir  # noqa: PLC0415
+
+        platforms = list_registered_platforms(
+            str(REPO_ROOT / "platforms"), include_archived=True
+        )
+        dirs = {
+            truth_target_dir("truth", platforms, alias, str(REPO_ROOT / "platforms"))
+            for alias in ("nx", "switch", "nintendo-switch")
+        }
+        self.assertEqual(dirs, {str(Path("truth") / "nintendo-switch")})
+
+    def test_writer_and_reader_call_one_function(self):
+        for module in ("generate_truth.py", "pipeline.py"):
+            source = (REPO_ROOT / "scripts" / module).read_text()
+            with self.subTest(module=module):
+                self.assertIn("truth_target_dir(", source)
+                self.assertNotIn('re.sub(\n            r"[^a-z0-9]+"', source)
+
+
 class TheListingCountsWhatTheFilterUses(unittest.TestCase):
     """--list-targets showed Batocera x86_64 with 198 cores; --target x86_64
     filters on 187 once _overrides.yml removes machine variants and launchers."""