Thanks for the reply and photo. Strange enough, I have an Edison in a box marked 'Ext Antenna' and the module still contains the ceramic chip antenna on it.. Not sure what is going on, I may try to do a signal strength experiment to sort it out.
Can you measure the resistance between the contact of the antenna and the connector on the Ext Antenna board?
An internal antenna board should have a 0 Om resistor between them acting as a wire.
All modules with the on-chip antenna show a short between one side of the chip antenna and the connector.
So I got another module in a brand new box marked 'Standard Power Off Board Antenna' and indeed it does not contain the on-chip antenna. So I believe the answer from Vincenze is correct in how to identify the external antenna version (look for the on-chip missing). I must have mixed up the modules during unpacking hence my confusion.