Supplementary criteria are the criteria in a benchmarking methodology where each such criterion may or may not be scored (or judged in some non-scoring way, depending on the wishes of the institution involved. Typically they cover issues not seen as universally and compellingly associated with "success" (whatever that means) in e-learning. See also scoring.
An example in Pick&Mix is supplementary criterion 57 "IPR in e-learning". Despite several recent reports from HEFCE and JISC on the importance of a good approach to handling intellectual property rights in e-learning, none of the three institutions in the Higher Education Academy Benchmarking Pilot of Pick&Mix decided to analyse this criterion - there were just too many other ones which in their view were a better use of limited resources to analyse. The strategic justification was that there are several exemplars of successful e-learning programmes where IPR was ignored or the issues "bought out" in a simplistic way. It des not mean that IPR is not important, just not as important as other issues crowding on to a VC's desk.