Calendar app raw data shows incorrect date for 2027 DST events

In Apple Calendar, data is stored in an SQLite database. When reading this data through another program, the date/time values of events (calendar items) are read as Unix dates, starting at January 1st 2001 (Unix usually uses 1.1.1970 as starting point).

I have encountered a new problem. When I use the Calendar app in 2026 to add a new calendar item for 2027 some time after the start of daylight savings time in Europe, the date-time-value used is one day before the intended date! (e.g. April 11 instead of April 12). In the Calendar app this is no problem, everything looks fine, but when reading the raw data directly, the date is off. This is regardless of whether it is an all-day event of if it has a specific start and end time.

I tried converting the date-time-value using an sqlite-function (modifier "unixepoch" "31 years") as well as using Java Calendar.add(Calendar.YEAR, 31) – same result.

Am I missing something? Why is Apple Calendar interpreting dates in 2027 DST differently all of a sudden?