There might be a few more points to make. How do screen dramas cope with a change of actor for the central character later in the series? Usually we have to just accept that it is the same character but a different actor. People make a big deal out of who is the new James Bond and that series has lost any chronological consistency or credibility.
Occasionally, there is another approach. In a British TV "Robin Hood" series, the guy who played Robin was due to leave so - Robin died at the end of the season. In the following season, the Merry Men continued as outlaws and were joined by a new guy called Robert who took a leading role and came to be known as "Robin Hood," thus explaining inconsistencies in the legend. See here.
In sf, there are a few other possibilities:
Time Lords regenerate and change their appearance;
in Fred Hoyle's and John Elliot's A For Andromeda and The Andromeda Breakthrough, the android was played by a different actress in the sequel but some science fictional explanation was devised for her changed appearance;
in Poul Anderson's third Dominic Flandry novel, Flandry has changed his face by "biosculp" but does not change it again so there would have to be one actor for dramatizations of the first two books and one other actor for the entire rest of the series.
In The Girl With The Dragon Tattoo, there are not only omissions of fictional events and plot elements but also clever rewrites to connect events in a different way with a shorter narrative, e.g., in the book, Blomkvist's daughter interprets apparent telephone numbers as Biblical references and Blomkvist works with Salander whereas, in the film, Salander interprets the numbers and works with Blomkvist, thus removing the daughter from the story. No doubt, similar stunts could be pulled with Anderson's lengthy series but I think that it would be better if every novel were to be serialized when adapted to screen so that nothing would have to be left out.