Several months ago I posted queries about the tz database to this discussion list as I investigated a series of errors triggered in software used to order and report clinical laboratory tests in our hospital network. Our main software system uses universal time for date& time of birth a recently added peripheral system (based on Android OS, and Java Joda-time that relies on the tz database) that triggered the peripheral system to freeze every few weeks. Investigation revealed that there were 10 years (between 1935 and 1945) in the America/Regina tz time zone data where the transition to daylight saving time occurred at midnight on spring transition dates. If our hospital (which is in the America/Regina time zone) encountered patients born on one of those spring daylight savings time transitions dates 1935-1945, the system froze, because the hour of birth was usually unknown and was assigned to midnight local time by default, and midnight local time on those dates does not map back to universal time. A software patch was quickly developed by the software provider and this susceptibility is now avoided. I understand now that this type of situation is well known to members of this group. I want to pass on a 'thank-you' to the tz database community for their helpful messages as this case was investigated. A description of this investigation was published today in the Journal of Applied Laboratory Medicine: "No Lab Tests" When You Are Born in The Twilight Zone: A Clinical Informatics Case Report. [ https://pubmed.ncbi.nlm.nih.gov/32728691/ | https://pubmed.ncbi.nlm.nih.gov/32728691/ ] best wishes, Andrew Dr. A.W. Lyon Dept Pathology and Laboratory Medicine University of Saskatchewan, SK, Canada