Modular Synth Panels

Am I missing something here?
This is a second run of boards, did you get permission from Don for
the first run? if so, why would you need permission for a second run
of the same board?
On another note, the basic idea and design was Don's, you have
modified the design and added other aspects to the circuit, so it is
no longer his design, but yours. 90% of the designs in DIY (and in
production synth modules) are based on something else, whether it is
someone else's circuit, a modification of the app notes for the IC, or
a circuit out of the old Electronotes, it doesn't matter, if you make
any changes to it, it is now your design, most of my designs are based
around the chip manufacturers app notes, or a circuit I found in
Electronotes, so according to your logic I should be asking the chip
manufacturers for their permission before I get any boards done up, or
I should spend years trying to track down the guy who submitted the
circuit to Electronotes 30 years ago, sometimes this "Intellectual
Property" can be pushed a bit to far. 
If you want to make a direct clone of a specific module
(panels,circuit,pcb) then yes, you should get the original designers
permission, otherwise I see no reason for it.

My 2 cents worth,
Dave