During our Migration to Pro we were trying to standardize all our date fields to be in UTC to match the editor tracking fields, that are mandatory UTC, but have date entry for all other fields using a time zone preference that is not UTC. Time zone preference is supported in a feature service. We were trying to use best practices to have a consistent time offset between all date fields. It was found that any date pre 2007 is not obeying the IANA logic for time zone conversion which is causing erroneous dates.
This example is all going to be shown as what the UI is seeing and not what the database is storing. Take for example Mar 9, 2006, in desktop it had no time stamp, in Pro that has become Mar 9, 2006 12:00am. When you view that in the service it is becoming Mar 8, 2006 11 am since the background time zone conversion is not obeying the logic for proper time zone conversion. This same bug is also prevalent in the Time Zone Conversion GP tool which has the same issue.
We have lots of legal dates that need to be correctly shown that are pre 2006 that we need to have faith are going to be handled correctly.