diff --git a/src/utils/tagManipulation.js b/src/utils/tagManipulation.js
index 53e5908..ccf5490 100644
--- a/src/utils/tagManipulation.js
+++ b/src/utils/tagManipulation.js
@@ -2,8 +2,6 @@ import validTagsList from "../../.github/actions/validTagsList.json";
 import possibleTagColors from "./tagColors.json";
 import { allLabNamesAndUrls } from "../data/labNamesUrls";
 
-const tagKeyNames = Object.keys(validTagsList);
-
 // Used in the filter menu to add/remove params
 // Used when clicking on a tag to remove all params and add only the one clicked
 export function updateSearchParamUrl(urlStringToUpdate, tagInput) {
@@ -29,56 +27,33 @@ export function getBackgroundColor(key) {
   return index >= 0 ? possibleTagColors[index] : "#6ebebd";
 }
 
-// Takes in a content collection object (e.g., projects or ecosystems) and returns an object of only the unique tag keys and unique tag values within each key
+// Takes in a content collection object (e.g., projects or ecosystems) and returns
+// an object of only the unique tag keys and unique tag values within each key
 // All returned keys and tags are lowercase
 // Keys are in the order set by validTagsList. Tags are in alphabetical order
 // Used to create the tag categories and tag option list in the filter menu
-export function extractUniqueTagsObject(contentCollectionObj) {
-  const uniqueTags = {};
-  //Ensure contentCollectionObj is always treated as an array, to handle cases where the length is 1
-  const normalizedCollection = Array.isArray(contentCollectionObj)
-    ? contentCollectionObj
-    : [contentCollectionObj];
+export function extractUniqueTagsObject(contentCollection) {
+    const uniqueTags = {};
+    const validTagKeys = Object.keys(validTagsList);
 
-  normalizedCollection.forEach((contentItem) => {
-    Object.entries(contentItem.data).forEach(([key, value]) => {
-      // tagKeyNames are the keys of validTagsList, imported at the top of the file
-      // If the current key is a value in tagKeyNames, we want to check if the key exists in uniqueTags
-      const isTagKey = tagKeyNames.some((tagKeyName) => tagKeyName === key);
-      if (isTagKey) {
-        //only process if the key has a value. User could have left it blank.
-        if (value) {
-          // process for if the value of key is an array (can also be a string - see else statement below)
-          if (Array.isArray(value)) {
-            value.forEach((tagValue) => {
-              // if the key doesn't exist in uniqueTags, add it and set it equal to the current tag value
-              if (!uniqueTags[key]) {
-                uniqueTags[key] = [tagValue];
-              } else {
-                // if the key does exist in uniqueTags, check whether the current tag value exists. If not, add the current tag value
-                if (!uniqueTags[key].includes(tagValue)) {
-                  uniqueTags[key].push(tagValue);
-                }
-              }
-            });
-          } else {
-            //process for if the value of key is a string - this is a valid tag input from users in the MD files.
-            //this is the same process as found in the forEach loop above
-            if (!uniqueTags[key]) {
-              uniqueTags[key] = [value];
-            } else {
-              if (!uniqueTags[key].includes(value)) {
-                uniqueTags[key].push(value);
-              }
-            }
-          }
-        }
+  // For each key, determine the union of all unique values associated with it
+  // (across all content items), excluding keys which aren't in validTagsList.
+  contentCollection = Array.isArray(contentCollection) ? contentCollection : [contentCollection];
+  contentCollection.forEach((contentItem) => {
+    Object.entries(contentItem.data).forEach(([key, tagValues]) => {
+      if (!validTagKeys.includes(key) || !tagValues || !tagValues.length) {
+        return;
       }
+      tagValues = Array.isArray(tagValues) ? tagValues : [tagValues];
+      tagValues.forEach((tv) => {
+        (uniqueTags[key] ??= new Set()).add(tv);
+      });
     });
   });
-  // Alphabetize the values in the array within each key
+
+  // Convert from Sets to sorted Arrays
   Object.keys(uniqueTags).forEach((key) => {
-    uniqueTags[key].sort();
+    uniqueTags[key] = Array.from(uniqueTags[key]).sort();
   });
   return uniqueTags;
 }
@@ -90,6 +65,7 @@ export function extractUniqueTagValueArray(projectData) {
 
   Object.entries(projectData).forEach(([key, value]) => {
     // If the current projectData key is a value in the tagKeyNames array, and the key has some associated value, add to uniqueTagsObj
+    const tagKeyNames = Object.keys(validTagsList);
     const isTagKey = tagKeyNames.some((tagKeyName) => tagKeyName === key);
     if (isTagKey) {
       if (value) {