We used to perform KBs in blood transfusion, but we finally got rid of them to haematology. The reason for this was because it was so unusual for us to come across a true positive (apart from the positive control, of course) that we felt that we were no longer able to guarantee competency, whereas, in those days, haematology were used to performing manual reticulocytes, and so could almost guarantee competency.
Nowadays, of course, retic counts are performed by automation, so their competency can no longer be guaranteed either (but we never accepted the KB's back!!!!!).
Since 2009 (