diff --git a/src/router.ts b/src/router.ts
index 153df62..4ef6479 100755
--- a/src/router.ts
+++ b/src/router.ts
@@ -568,16 +568,12 @@ export async function registerAllListeners() {
     try {
       // privateFields is only used if newData contains new fields
       // roles can be empty meaning that roles from the last commited state are kept
-      const { processId, lastStateId, newData, privateFields, roles, accessToken } = event.data;
+      const { processId, newData, privateFields, roles, accessToken } = event.data;
 
       if (!accessToken || await !tokenService.validateToken(accessToken, event.origin)) {
         throw new Error('Invalid or expired session token');
       }
 
-      if (!isValid32ByteHex(lastStateId)) {
-        throw new Error('Invalid last state id');
-      }
-      
       // Check if the new data is already in the process or if it's a new field
       const process = await services.getProcess(processId);
       if (!process) {
@@ -587,36 +583,50 @@ export async function registerAllListeners() {
       if (!lastState) {
         throw new Error('Process doesn\'t have a commited state yet');
       }
-      if (lastState.state_id !== lastStateId) {
-        throw new Error('Process has been updated');
-      }
-      console.log('🚀 ~ handleUpdateProcess ~ lastState:', lastState);
+      const lastStateIndex = services.getLastCommitedStateIndex(process);
+      if (lastStateIndex === null) {
+        throw new Error('Process doesn\'t have a commited state yet');
+      } // Shouldn't happen
 
       const privateData: Record<string, any> = {};
       const publicData: Record<string, any> = {};
 
       for (const field of Object.keys(newData)) {
         console.log('🚀 ~ handleUpdateProcess ~ newData[field]:', newData[field]);
-        if (lastState.pcd_commitment[field]) {
-          // is it a private field ?
-          if (lastState.public_data[field]) {
-            // Add it to public data  
-            publicData[field] = newData[field];
-          } else {
-            // Add it to private data
-            privateData[field] = newData[field];
-          }
-        } else {
-          // is it supposed to be private ?
-          if (privateFields.includes(field)) {
-            // Add it to private data
-            privateData[field] = newData[field];
-          } else {
-            // Add it to public data
-            publicData[field] = newData[field];
-          }
-          // For new fields we should check that roles have been modified accordingly, otherwise the state would be impossible to commit
+        // Public data are carried along each new state
+        // So the first thing we can do is check if the new data is public data
+        if (lastState.public_data[field]) {
+          // Add it to public data
+          publicData[field] = newData[field];
+          continue;
         }
+
+        // If it's not a public data, it may be either a private data update, or a new field (public of private)
+        // Caller gave us a list of new private fields, if we see it here this is a new private field
+        if (privateFields.includes(field)) {
+          // Add it to private data
+          privateData[field] = newData[field];
+          continue;
+        }
+
+        // Now it can be an update of private data or a new public data
+        // We check that the field exists in previous states private data
+        for (let i = lastStateIndex; i >= 0; i--) {
+          const state = process.states[i];
+          if (state.pcd_commitment[field]) {
+            // We don't even check if it's a public field, we would have seen it in the last state
+            privateData[field] = newData[field];
+            break;
+          } else {
+            // This attribute was not modified in that state, we go back to the previous state
+            continue;
+          }
+        }
+
+        if (privateData[field]) continue;
+
+        // We've get back all the way to the first state without seeing it, it's a new public field
+        publicData[field] = newData[field];
       }
 
       // We'll let the wasm check if roles are consistent