I guess this must be testable. I’m given to think your assumption is possible in error.
As I have a moment, I’m looking at https://www.edarabia.com/school-holidays-london/ and it says that Feb 17-20 2020 is the Spring Half Term.
I’m picking the 674 bus from https://en.wikipedia.org/wiki/List_of_bus_routes_in_London#List_of_routes
However, when I try to Jounrey Plan I dont see the 674 in the output, no matter what…
Hurah? However I change the date to the week before and the answer is the same.
Looking at Google Maps, it’s the same too, no 6XX buses.
From this I might conculde that you don’t see Schoool Buses in the Journey Planner.
Can you @mjcarchive see a 600-699 bus route in the Journey Planner?