After watching the thirteen films in the Marvel Cinematic Universe, I've been wondering if there is a longer running series of films that maps out a continuous storyline.
I've found this article on Wikipedia, but I am unsure if any of these film series have reboots, or even if they follow a continuous plotline/timeline.
The James Bond series of films features a reboot, but even before Casino Royale there didn't seem to be much of a continual plotline across the entire series of films (despite the recurring characters, organisations and themes).
To explain what I mean by continuous plotline, I am going by the following criteria:
The important part here is the continuous timeline of events. If a film can be placed somewhere in the timeline of a series without causing issues (eg. characters being revived without explanation, previously destroyed places suddenly restored without explanation, massive jumps in time for the setting and yet the characters don't age without explanation), then it is part of the continuous timeline. Otherwise that film breaks the timeline and cannot be included.
I am more than happy to accept parts of a film series. For example if twenty of the thirty or more Godzilla films all follow these criteria, then I would accept those twenty films as a continuous plotline.
I can think of several film series that fit these criteria, the Star Wars and Harry Potter film series are two examples. But I am looking for the longest series of films that fits my criteria of a continuous plotline or timeline of events.
Films don't have to be direct sequels/prequels to fit into my criteria - films in the same setting but chronologically spread out, and therefore with different characters would fit the bill so long as they kept to a continuous timeline of events. Also, I would accept foreign language films and films that are TV movies or straight to DVD films.
According to Wikipedia's entry for Blondie (the comic strip), of the 28 movies made based on the strip, at least the first 14 were a continuous series meeting your definition:
Columbia was careful to maintain continuity, so each picture progressed from where the last one left off. Thus the Bumstead children grew from toddlers to young adults onscreen. [...]
In 1943 Columbia felt the series was slipping, and ended the string with It's a Great Life and Footlight Glamour, deliberately omitting "Blondie" from the titles to attract unwary moviegoers. After 14 Blondies, stars Singleton and Lake moved on to other productions. During their absence from the screen, Columbia heard from many exhibitors and fans who wanted the Blondies back. The studio reactivated the series, which ran another 14 films until discontinued permanently in 1950.
So this is definitely 14, and possibly as many as all 28; I note that the entry for Larry Sims (the child actor who plays Dagwood & Blondie's son Alexander) is listed as appearing in all 28 films.
The Up documentary series currently consists of eight films spanning 48 years. The original film, Seven Up!, was released in 1964 and featured interviews with several 7-year-old British children from a variety of backgrounds.
Since then, the original filmmakers have produced new documentaries revisiting the subjects every seven years. The most recent film in the series is 56 Up! released in 2012, and there's every reason to believe that the series will continue on schedule.
It is The Land Before Time. There have been 14 movies in the series, but the 13th one is reboot. So, if we don't count it, there are still 12.
The Land Before Time is a franchise of Universal Studios animated films centered on dinosaurs. The series began in 1988 with The Land Before Time, directed and produced by Don Bluth and executive produced by George Lucas and Steven Spielberg.
Old Answer (after pointed out in comment)
This can be Carry On (1958-1992).
The Carry On franchise primarily consists of a sequence of 31 low-budget British comedy motion pictures (1958–92), four Christmas specials, a television series of thirteen episodes, and three West End and provincial stage plays. The films' humour was in the British comic tradition of the music hall and bawdy seaside postcards. Producer Peter Rogers and director Gerald Thomas drew on a regular group of actors, the Carry On team, that included Sidney James, Kenneth Williams, Charles Hawtrey, Joan Sims, Kenneth Connor, Peter Butterworth, Hattie Jacques, Terry Scott, Bernard Bresslaw, Barbara Windsor, Jack Douglas and Jim Dale.
NOTE: There may be many other series in other languages, but one can only say confirm if he/she has watched it.