In at least 2 of the maps, scoring after the end of the game will not work.
On the Great Britain map, you get bonus points during play :
From the moment you have purchased the «Boiler Lagging» card,
you score 1 extra point for each route that you claim.
Also, from the moment you have purchased the «Steam Turbines» card,
you score 2 extra points for each Ferry route that you claim.
When combined with «Boiler Lagging», you score 3 points for each Ferry route that you claim.
From the rules:
«Some players like to add up the points for the routes they claim
at game end, rather than each time a route is claimed. Because the
score for some routes may be affected by technologies such as
the Boiler Lagging or the Steam Turbines, waiting until the end
to compute Routes points doesn’t work in this expansion.»
Reference : Rules for Ticket To Ride United Kingdom : https://ncdn0.daysofwonder.com/tickettoride/en/img/tt-mc5_uk_rules_2015.pdf
Something similar occurs in TTR - Africa.
From the rules :
«When Claiming a Route, in addition to playing Train car cards, a player may also simultaneously play some of the Terrain cards in front of him to double the points value of the Route he’s claiming.»
At the end of the game you will have no way of knowing which Terrain Card doubled the point value of any route.
Reference : Rules for Ticket To Ride The Heart Of Africa : https://ncdn0.daysofwonder.com/tickettoride/en/img/tt_africa_rules_2015.pdf
The only way that I have found to not forget to score as you play is to use the «Talking Feather» (or some other unique objet) used by many native American Indian tribes. One can use, for example, the letter-holder from Scrabble, which reminds me of a rail. Whoever has the object plays. In order to start your turn, you must receive the object from the previous player. That action reminds everyone to score the route that has been claimed before the player starts.