This was created inadvertently. I forgot to spoof the MAC address when setting up a new Pi. The original Pi had stats going back a year and I didn’t want to lose them.
It would be nice if FlightAware used sharing keys like other sites. 
How would FlightAware identify a Pi A which has no ethernet interface??
I think they fall off automatically after 30 days of no activity. (And a Pi with no Ethernet interface would have a problem connecting to the network in the first place,
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Thanks for the reply. 
I’ve had a dormant site that stayed “alive” longer than 30 days.
The Pi A can use a USB wireless adapter.
Looks like the A and the CM both get MAC’s assigned to them, even without the ethernet port. (If not, the Wifi module would have a MAC…) https://www.raspberrypi.org/forums/viewtopic.php?f=98&t=80016
The software looks at the hardware MAC address, it doesn’t use the wireless MAC for FA.