should be a working solution

src/main/java/gov/nasa/pds/tools/util/FileReferencedMapList.java

@@ -49,11 +49,9 @@ public class FileReferencedMapList {
   // Class to hold a map of every labels that referenced a physical file.
   // If a file is referenced by more than one label, an error should be thrown.
   class FileReferencedMap {
-    private URL url = null;
     private List<String> labelNames = new ArrayList<>();
 
-    public FileReferencedMap(URL url) {
-      this.url = url;
+    public FileReferencedMap() {
     }
 
     public void setLabels(String labelName) {
@@ -86,7 +84,7 @@ public FileReferencedMap setLabels(URL url, String labelName) {
     } else {
       // If fileReferencedMaps does not contain an existing, url, create a new
       // FileReferencedMap and add labelName to the new empty list.
-      fileReferencedMap = new FileReferencedMap(url);
+      fileReferencedMap = new FileReferencedMap();
       fileReferencedMap.setLabels(labelName);
       fileReferencedMaps.put(url, fileReferencedMap);
     }

src/main/java/gov/nasa/pds/tools/validate/CrossLabelFileAreaReferenceChecker.java

@@ -0,0 +1,58 @@
+package gov.nasa.pds.tools.validate;
+
+import java.io.IOException;
+import java.nio.file.Path;
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.List;
+import javax.xml.parsers.DocumentBuilderFactory;
+import javax.xml.parsers.ParserConfigurationException;
+import javax.xml.transform.dom.DOMSource;
+import org.w3c.dom.Document;
+import org.xml.sax.SAXException;
+import gov.nasa.pds.tools.util.LabelUtil;
+
+public class CrossLabelFileAreaReferenceChecker {
+  final private static HashMap<String,List<String>> knownRefs = new HashMap<String,List<String>>();
+  private static String resolve (String name, ValidationTarget target) {
+    if (!name.startsWith ("/")) {
+      name = Path.of(target.getUrl().getPath()).getParent().resolve(name).toString();
+    }
+    return name;
+  }
+  /**
+   * @param name - the file being referenced by the file area
+   * @param target - the label being validated
+   * @return true if name and target are unique and only known references and false otherwise
+   * All of these exceptions should not happen because they are getting the LID from the target.
+   * Would not have made it this far if that could not have happened already, So, just pass them
+   * back to the called and let them handle it with their own generic exception handler/message.
+   * @throws IOException
+   * @throws ParserConfigurationException
+   * @throws SAXException
+   */
+  public static boolean add (String name, ValidationTarget target) throws IOException, ParserConfigurationException, SAXException {
+    boolean success = false;
+    DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
+    Document xml = dbf.newDocumentBuilder().parse(target.getUrl().openStream());
+    DOMSource domSource = new DOMSource(xml);    
+    for (String lid : LabelUtil.getLogicalIdentifiers (domSource, target.getUrl())) {
+      if (lid.contains("::")) {
+        lid = lid.substring (0, lid.indexOf("::"));
+      }
+      if (!knownRefs.keySet().contains (resolve(name, target))) {
+        knownRefs.put(resolve(name, target), (List<String>)Arrays.asList(lid, target.getUrl().getPath()));
+        success = true;
+      } else {
+        success = false;
+      }
+    }
+    return success;
+  }
+  public static String getOtherId (String name, ValidationTarget target) {
+    return knownRefs.get(resolve(name, target)).get(0);
+  }
+  public static String getOtherFilename (String name, ValidationTarget target) {
+    return knownRefs.get(resolve(name, target)).get(1);
+  }
+}

src/main/java/gov/nasa/pds/tools/validate/rule/pds4/FileReferenceValidationRule.java

@@ -45,6 +45,7 @@
 import gov.nasa.pds.tools.util.PDFUtil;
 import gov.nasa.pds.tools.util.Utility;
 import gov.nasa.pds.tools.util.XMLExtractor;
+import gov.nasa.pds.tools.validate.CrossLabelFileAreaReferenceChecker;
 import gov.nasa.pds.tools.validate.ProblemDefinition;
 import gov.nasa.pds.tools.validate.ProblemType;
 import gov.nasa.pds.tools.validate.ValidationProblem;
@@ -280,6 +281,15 @@ private boolean validate(NodeInfo xml) {
                 name = child.getStringValue();
                 this.fileMapping.put(name, "");
                 LOG.debug("FileReferenceValidationRule:validate:name {}", name);
+                if (!CrossLabelFileAreaReferenceChecker.add (name, target)) {
+                  this.getListener().addProblem(
+                      new ValidationProblem(
+                          new ProblemDefinition(ExceptionType.ERROR, ProblemType.DUPLICATED_FILE_AREA_REFERENCE,
+                              "This file area references " + name + " that is already used by label "
+                              + CrossLabelFileAreaReferenceChecker.getOtherId(name, target)
+                              + " in file " + CrossLabelFileAreaReferenceChecker.getOtherFilename(name, target)),
+                          target, fileObject.getLineNumber(), -1));
+                };
               } else if ("md5_checksum".equals(child.getLocalPart())) {
                 checksum = child.getStringValue();
                 LOG.debug("FileReferenceValidationRule:validate:checksum {}", checksum);

src/test/resources/features/developer.feature

@@ -10,7 +10,7 @@ Scenario Outline: Execute validate command for tests below.
  | testName                                             | testDir     | messageCount | messageText         | problemEnum     | resourceDir          | reportDir     | commandArgs                                                                | refOutputValue | 
 
 # Validate#755
-|"NASA-PDS/validate#755 Detect and report file areas referencing same file" | "github755" | 1 | "1 errors expected" | "DUPLICATED_FILE_AREA_REFERENCE" | "src/test/resources"   | "target/test" | "-r {reportDir}/report_github755.json -s json -skip-content-validation -t {resourceDir}/github755/m221011.0013.xml {resourceDir}/github755/m221011.0014.xml {resourceDir}/github755/m221011.0015.xml {resourceDir}/github755/m221011.0030.xml" | "report_github755.json" |
+|"NASA-PDS/validate#755 Detect and report file areas referencing same file" | "github755" | 2 | "2 errors expected" | "DUPLICATED_FILE_AREA_REFERENCE" | "src/test/resources"   | "target/test" | "-r {reportDir}/report_github755.json -s json -skip-content-validation -t {resourceDir}/github755/m221011.0013.xml {resourceDir}/github755/m221011.0014.xml {resourceDir}/github755/m221011.0015.xml {resourceDir}/github755/m221011.0030.xml" | "report_github755.json" |
 |"NASA-PDS/validate#755 No common file referenced" | "github755" | 0 | "0 errors expected" | "totalErrors" | "src/test/resources"   | "target/test" | "-r {reportDir}/report_github755.1.json -s json -skip-content-validation -t {resourceDir}/github755/m221011.0013.xml {resourceDir}/github755/m221011.0015.xml" | "report_github755.1.json" |
 
 # Validate#754