@Kevin_Z OK- it is odd that one has a 6 character device ID. But, does it really matter that the the device ID's are not the last four characters of the MAC address? Now I know there is a disconnect...

@johnnyC Thankyou for your response to my post. The Extenders are all connected through my household electricity wiring via 13A sockets. I hereby attach a screenshot of the TP-link utility network...

I have the TL WPA4220Kit with four range extenders - all working with the occassional glitch. My query concerns the labelling of the devices. Three of the extenders had labels showing a Device ID...