In https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=714058#55 John Dunning writes on 4/May/2015:

"Hi all.  I gather that the preference is to license CC65 and
associated technologies under the zlib license.  I hereby give my
approval for any software written by me as part of CC65 and associated
technologies under the zlib license."

The above together with the fact that all subsequent work on cc65 was already licensed under the zlib license means that cc65 can now be licensed altogether under the zlib license.