diff --git a/handbook/survey/caveentry.html b/handbook/survey/caveentry.html
index 4ff33ae4f..c471edfd6 100644
--- a/handbook/survey/caveentry.html
+++ b/handbook/survey/caveentry.html
@@ -153,6 +153,9 @@ So each field you fill in on the form may contain arbitrary HTML. Be careful!</p
 <h2>List of New Cave/Cave_data fields</h2>
 <p>The full list of fields is documented: <a href="caveentryfields.html">the full list of data-entry fields</a> when creating a cave.
 
+  <h2>Wrong survey area? 1626 v 1623 ?</h2>
+<p>You create a new cave with the form and can set the area, either 1623 or 1626, but if you get it wrong, then re-editing the cave online and attempting to change that field will appear to work, but won't really. You need to get a nerd with a "bulk update laptop" to rename the files in cave_data and entrance_data too.
+
   <h2>If things go wrong</h2>
 <p>Tell a nerd, or post to the "expo" Signal group, or the Matrix "Website" room <em>immediately</em>. A broken edit can block all the forms working on the website: for Caves, Entrances, Logbook entries, Handbook edits.
   <h3>Tidying up and committing broken edits</h3>