The two weekend Kitchener trains are still in the most recent GTFS feed (which was updated on Wednesday, when the new schedules were uploaded). In fact it appears they're running Christmas and Boxing Day, which makes sense since GO runs weekend service on stat holidays. As
@WB62 said, early published schedules are known for having errors.
To expand on what
@Allandale25 has said, GO is now saying Kitchener, Lakeshore West and Lakeshore East trains will be running hourly on weekend/stat holidays from the 21st to the 5th. Outside of rush hour on weekdays, Lakeshore East and West are also scheduled for hourly-only service (as seen in the PDFs).
Finally, according to the most recent GTFS feed, it looks like GO is treating January 2nd as a stat holiday for the rail network (buses are running on weekday schedules).