The CBOE never had the whole market for options, some 10 years ago they were at 45%. The AEX has a bunch of options on various ETF and QQQ as well, which I am not interested in counting in an EPC. My guess is that the decrease in the fraction of the CBOE is correlated with the large increase in trading in artificial stocks (like the ETF, or other "stock instruments" like TLT that really represent either indices, sectors or even interest rates). Options on "artificial stocks" are counted in EPC when "All equity options" are counted. On the CBOE, the QQQ is the major non real equity option contributors, and when it is excessively high (difference between Puts and calls) exceeds 40,000 contracts, I take these out to come with the "Virgin EPC. I am therefore not concerned that now the CBOE represents only some 30% of all options traded, their EPC is still closer t reality than the "universal" EPC that includes all these artificial equity options.
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