diff --git a/code/robots.py b/code/robots.py
index 0281559..3a37eea 100755
--- a/code/robots.py
+++ b/code/robots.py
@@ -34,6 +34,25 @@ default_values = {
 }
 default_value = "Unclear at this time."
 
+def existing_key(existing_content, name: str) -> str:
+    """Return the key robots.json already uses for this agent, ignoring case.
+
+    robots.txt user-agent matching is case-insensitive, so two entries whose
+    names differ only in case are the same crawler. knownagents.com has changed
+    the capitalisation of a name before now, and keying off the scraped name
+    added a second entry rather than updating the first, which both duplicated
+    the User-agent line in every generated file and left the curated operator
+    and respect values behind on the old key.
+    """
+    if name in existing_content:
+        return name
+    lowered = name.lower()
+    for key in existing_content:
+        if key.lower() == lowered:
+            return key
+    return name
+
+
 def consolidate(existing_content, name: str, field: str, value: str) -> str:
     # New entry
     if name not in existing_content:
@@ -77,6 +96,7 @@ def updated_robots_json(soup):
         for agent in section.find_all("a", href=True):
             name = agent.find("div", {"class": "agent-name"}).get_text().strip()
             name = clean_robot_name(name)
+            name = existing_key(existing_content, name)
 
             desc_tag = agent.find("div", {"class": "description"})
             if desc_tag is not None:
diff --git a/code/tests.py b/code/tests.py
index 0006f5d..1e9adb2 100755
--- a/code/tests.py
+++ b/code/tests.py
@@ -7,6 +7,7 @@ import unittest
 
 from robots import (
     consolidate,
+    existing_key,
     default_value,
     default_values,
     json_to_caddy,
@@ -203,6 +204,19 @@ class TestConsolidate(unittest.TestCase, RobotsUnittestExtensions):
         self.assertEqual("Rosie is the robot maid from The Jetsons, an American animated sitcom", 
                          consolidate(existing, "rosie", "description", "Rosie is the robot maid from The Jetsons, an American animated sitcom"))
 
+class TestExistingKey(unittest.TestCase):
+    def test_exact_match_wins(self):
+        existing = {"Rosie": {}, "rosie": {}}
+        self.assertEqual("rosie", existing_key(existing, "rosie"))
+
+    def test_matches_ignoring_case(self):
+        existing = {"Rosie": {"operator": "George Jetson"}}
+        self.assertEqual("Rosie", existing_key(existing, "rosie"))
+
+    def test_unknown_name_is_returned_unchanged(self):
+        self.assertEqual("rosie", existing_key({}, "rosie"))
+
+
 if __name__ == "__main__":
     import os
     os.chdir(os.path.dirname(__file__))