After much soul-searching about question 53 (the yield beta one), searching the forum and all that I checked the CFA site as an afterthought. They have an errata for the mock exams Mock Exam: In the Durham case scenario the fifth paragraph beginning “Groton has identified a U.S. Treasury…” was replaced with the following paragraph: o “Groton has identified, as the CTD bond, a U.S. Treasury futures contract with a duration of 6.5 priced at $110,425. The conversion factor for the CTD bond is 0.9177 and the yield beta is 1.00. Groton tells the committee that the yield beta captures the relation between the CTD bond and the futures contract.” So all the theories about when yield beta is NOT to be used may not really be relevant. Why they have to post an errata without correcting the PDF that is on their own site I do not understand.