BA/KL
Yes BA have reduced the schedules from 4 to 3 on Saturdays for about 4 weeks. It returns to 4 in a week or so.
Weekday has always this summer been scheduled to 6 but there have been one or two cancellations due to weather etc. But they tend to put a 321 on the next flight after the cancelled 319/320. Happened to me a couple of weeks ago.
KL do use 738 on some flights now generally the teatime to AMS. In the school hols the 738/739 appear on other flights also. I believe the type is confirmed about 2 weeks in advance.