Actually, both nacks and acks indicate a valid path

src/or/rendclient.c

@@ -361,6 +361,10 @@ rend_client_introduction_acked(origin_circuit_t *circ,
 #endif
   tor_assert(circ->rend_data);
 
+  /* For path bias: This circuit was used successfully. Valid
+   * nacks and acks count. */
+  circ->any_streams_succeeded = 1;
+
   if (request_len == 0) {
     /* It's an ACK; the introduction point relayed our introduction request. */
     /* Locate the rend circ which is waiting to hear about this ack,
@@ -378,9 +382,6 @@ rend_client_introduction_acked(origin_circuit_t *circ,
        * it to specify when a circuit entered the
        * _C_REND_READY_INTRO_ACKED state. */
       rendcirc->base_.timestamp_dirty = time(NULL);
-      
-      /* For path bias: This circuit was used successfully */
-      circ->any_streams_succeeded = 1;
     } else {
       log_info(LD_REND,"...Found no rend circ. Dropping on the floor.");
     }