diff --git a/xos/synchronizer/pull_steps/pull_olts.py b/xos/synchronizer/pull_steps/pull_olts.py
index 7c2cadf..8e33642 100644
--- a/xos/synchronizer/pull_steps/pull_olts.py
+++ b/xos/synchronizer/pull_steps/pull_olts.py
@@ -114,11 +114,10 @@
             try:
                 if "host_and_port" in olt:
                     model = OLTDevice.objects.filter(device_type=olt["type"], host=host, port=port)[0]
-                    log.debug("[OLT pull step] OLTDevice already exists, updating it", device_type=olt["type"], host=host, port=port)
+                    log.debug("[OLT pull step] OLTDevice already exists, updating it", device_type=olt["type"], id=model.id, host=host, port=port)
                 elif "mac_address" in olt:
                     model = OLTDevice.objects.filter(device_type=olt["type"], mac_address=mac_address)[0]
-                    log.debug("[OLT pull step] OLTDevice already exists, updating it", device_type=olt["type"], mac_address=mac_address)
-
+                    log.debug("[OLT pull step] OLTDevice already exists, updating it", device_type=olt["type"], id=model.id, mac_address=mac_address)
 
                 if model.enacted < model.updated:
                     log.debug("[OLT pull step] Skipping pull on OLTDevice %s as enacted < updated" % model.name, name=model.name, id=model.id, enacted=model.enacted, updated=model.updated)
@@ -136,6 +135,7 @@
                 if olt["type"] == "simulated_olt":
                     model.host = "172.17.0.1"
                     model.port = 50060
+                    log.debug("[OLT pull step] OLTDevice is new, creating it. Simulated")
                 elif "host_and_port" in olt:
                     [host, port] = olt["host_and_port"].split(":")
                     model.host = host
@@ -151,6 +151,8 @@
                 nni_ports = [p for p in olt_ports if "ETHERNET_NNI" in p["type"]]
                 if not nni_ports:
                     log.warning("[OLT pull step] No NNI ports, so no way to determine uplink. Skipping.", device_type=olt["type"], host=host, port=port)
+                    model.device_id = olt["id"]  # device_id must be populated for delete_olts
+                    updated_olts.append(model)
                     continue
 
                 # Exctract uplink from the first NNI port. This decision is arbitrary, we will worry about multiple
@@ -160,10 +162,44 @@
                 # Initial admin_state
                 model.admin_state = olt["admin_state"]
 
+            # Check to see if Voltha's serial_number field is populated. During Activation it's possible that
+            # Voltha's serial_number field may be blank. We want to avoid overwriting a populated data model
+            # serial number with an unpopulated Voltha serial number. IF this happened, then there would be
+            # a window of vulnerability where sadis requests will fail.
+
+            if olt['serial_number'] and model.serial_number != olt['serial_number']:
+                # Check to see if data model serial number is already populated. If the serial number was
+                # already populated, and what we just learned from Voltha differs, then this is an error
+                # that should be made visible to the operator, so the operator may correct it.
+                if model.serial_number:
+                    log.error("Serial number mismatch when pulling olt. Aborting OLT Update.",
+                              model_serial_number=model.serial_number,
+                              voltha_serial_number=olt['serial_number'],
+                              olt_id=model.id)
+                    model.backend_status = "Incorrect serial number"
+                    model.backend_code = 2
+                    model.save_changed_fields()
+                    # Have to include this in the result, or delete_olts() will delete it
+                    updated_olts.append(model)
+                    # Stop processing this OLT
+                    continue
+
+                # Preserve existing behavior.
+                # Data model serial number is unpopulated, so populate it.
+
+                # TODO(smbaker): Consider making serial_number a required field, then do away with this.
+                #                Deferred until after SEBA-2.0 release.
+
+                log.info("Pull step learned olt serial number from voltha",
+                         model_serial_number=model.serial_number,
+                         voltha_serial_number=olt['serial_number'],
+                         olt_id=model.id)
+
+                model.serial_number = olt['serial_number']
+
             # Adding feedback state to the device
             model.device_id = olt["id"]
             model.oper_status = olt["oper_status"]
-            model.serial_number = olt['serial_number']
 
             model.volt_service = self.volt_service
             model.volt_service_id = self.volt_service.id
@@ -275,8 +311,8 @@
             if model.enacted < model.updated:
                 # DO NOT delete a model that is being processed
                 log.debug("[OLT pull step] device is not present in VOLTHA, skipping deletion as sync is in progress", device_id=o.device_id,
-                         name=o.name)
+                          name=o.name)
                 continue
 
-            log.debug("[OLT pull step] deleting device as it's not present in VOLTHA", device_id=o.device_id, name=o.name)
+            log.debug("[OLT pull step] deleting device as it's not present in VOLTHA", device_id=o.device_id, name=o.name, id=o.id)
             model.delete()