I have read in in the original paper that in the year 1983 a research group in Kiel, Germany (that's where the Ki- in the name comes from) developed monoclonal mouse antibodies against Hodgkin lymphoma cells in multiple 24-well plates. If I understand correctly they were able to isolate antibodies from 63 wells and divided them into 493 microtiters into several 96-well microtitre plates. Of these 493 titres, 164 cell batches were chosen for further investigation and expanded. Somehow Ki-67 emerged from there, but why this number? Who gave it that name and why?
A teacher once told us in med school, the cells producing the antibodies were found in well 67, but I cannot find any source to back up that claim.