Numerous London routes have been shortened or split over the years, the theory being that shorted routes are easier to regulate in heavy/ congested traffic.
Yes.
Route 12 is worth a mention - until the early 70s, on paper from South Croydon to Willesden Junction (with peak extensions to Park Royal) although I don't think any buses ran the full length of the route then. Even in to the mid 1980s, the route was Norwood Junction - Willesden Junction, although again buses running the full route were a rarity. I have a vague recollection of travelling with parent from Forest Hill, and it took some time for parent to realise at that time of day / week, there weren't any buses from that far south to wherever we were trying to get to, even though that was on the 12 route. I also understand it was the last London route to be scheduled completely manually, as the computer system in place then couldn't handle the number of garages involved.
And 141 from Grove Park to Wood Green (previously to Winchmore Hill) is worth a mention, although again through buses end to end were a rarity, and for some years there was a gap in the middle on Saturdays, as it was split Wood Green - Moorgate and Grove Park - Elephant (think there may have been early morning journeys as far as Farringdon Street for homeward print workers when 'Fleet Street' was still based in and around the area.) Although at a later stage, buses only ran through on Saturdays, bringing Metrobuses in to SE London.
That's another angle (as well as the regulation / reliability argument) for shorter routes in London now - traditionally, many (although not all) of the longer routes had multiple garages along or near the line of route, which is more difficult post privatisation / tendering.
In Thames Valley land -
Route 1 was historically Newbury - Reading - Maidenhead. The Newbury end is broadly now Reading Buses route 1, the Maidenhead end only runs a few journeys on Saturdays as (new) Thames Valley 127
Route 2 was historically Reading - Bracknell - Windsor, and 3 Reading - Wokingham - Camberley. In the 1990s Bee Line era, this had become a group of routes in the 190+ sequence, some extending as far east as Sunningdale and Slough (and briefly via Slough to Heathrow.) Reading - Bracknell is now Reading Buses 4 / X4, east of Bracknell is now (new) Thames Valley territory.
Route 20 was Windsor - Maidenhead - High Wycombe, now split at Maidenhead.
The 1933 London Transport red (central) and green (country) bus areas didn't quite match what became Greater London in 1970. Many country bus / London Country routes have been split around the TFL / shire county boundary - 480 used to be Erith to Gravesend (Valley Drive) but the London end became 428, for example. There must be quite a few others, and similarly some London Transport (central bus) routes that extended beyond Greater London also got cut back - the 279 used to run beyond Waltham Cross to Hammond Street, which I think was the last Routemaster route outside the GLC area.
Although there are a few opposites to that - route 96 extending to Bluewater (along with 428 and 492, which both are descendants of green bus routes.)
The current route 31 from Cuckfield to Uckfield used to go from Cuckfield to Hurst Green but has since been cut back and that journey now requires three separate routes.
Southdown (in some cases joint with Maidstone and District) had some very long routes - including the 'Heathfield Pool' which included (from memory) Tunbridge Wells to Eastbourne and Hastings, and route 122 from Gravesend to Brighton via Tunbridge Wells. I have read that while buses worked through, the bus crews never crossed Tunbridge Wells on route 122 and would drive the other company's buses as part of their duty.
The Gravesend - Medway route of Maidstone and District (then route 26) continued to Sittingbourne, which must be at least 2 routes now.
