The Cornell statement in the flier you are referring to is unclear in that it does not specifically say both tests. Cornell has traditonally not superscored ACT tests and thus doing so now would be a change in policy. It is possible its position has changed, but I would not necessarily make that conclusion without a more definite statement, and contacting Cornell for an answer may be advisable.
Williams seems to be a college that apparently likes having applicants left in the dark. Williams itself has made conflicting statements on its site over the years on superscoring the ACT, e.g., there was a statement from 2011 that said it did and then one from 2012 that said it did not, but both statements have been gone from the site since 2013. Some have reported in years past being told by an admission’s officers that Williams does superscore while others have been told otherwise. The current site says nothing either way. In a statement addressing the new SAT to begin next March, it says it superscores the SAT but will not do so across the old and new SAT if applicants next year submit both, but again says nothing about the ACT. In other words, you likely have to contact Williams to determine the issue but even then I am not sure you will get the correct answer.