Again, this is nitpicking, but a LOT of stuff on BTTF forums IS nitpicking after all!
Basically, this is about the Citizen Brown timeline, and more to the point, its history.
In a throwaway line in Ep 4, FCB Doc mentions having a secret lab at Clayton Ravine...at which point Marty mentions Clara and tells FCB Doc about how she's supposed to be his wife in the other timeline(s). From the naming of the ravine, the obvious implication is that since the Delorean was never invented in this timeline, Doc never travelled back to 1885 and thus the original sequence of events, with Clara falling into the ravine, was restored. And on the surface it makes perfect sense...considering the fact that there is other evidence of the 'original histories' being restored; for instance, George and Lorraine are back to their loser selves from the original Twin Pines timeline, since they were never influenced by Marty in 1955. And yet, it seems to conflict with how the ripple effect, and alternate timelines, are portrayed in the trilogy...
Now, based on my understanding of the trilogy, the implication is that at any given point of time, the future is 'not written', and that the actions of a time traveller from the future (or with knowledge of the future) can change the course of the future (i.e. his/her past). As the future changes, objects brought back from the future (photos, newspapers etc) are changed by the 'ripple effect' to reflect the new timeline...and in extreme cases, people from the future may be erased from existence if they do not exist in the 'new future' (as Marty nearly was in BTTF1). The idea is that the ripple effect changes the future and affects objects and people from the future. So, if in 1955, something is done to change 1985, then the ripple effect moves forward from 1985, altering 1985, as well as objects in 1955 which originate from 1985.
However, I think the 1955 segment of BTTF2 clearly implies that while the time traveller, while in the past, can change the future, he cannot change anything in the past from BEFORE his 'arrival point' in the past. This explains why we see Marty from BTTF1 in the background in BTTF2. Old Biff arrived on the morning of November 12th 1955, and his actions radically altered 1985, such that the Delorean was never invented and Marty never travelled back in time...yet, this did not erase the actions of Marty from the original timeline since November 5th 1955 onwards, because Marty's arrival on Nov. 5th, his interfering with his parents meeting, the manure truck crash et all are all part of the 'past' at the point when Old Biff has arrived in 1955...his actions do not affect events prior to the morning of November 12th 1955.
And yet, the Game contradicts this...how? Simply by saying that Clara died falling into the ravine in 1885, in the FCB timeline.
Look at it this way. Marty and Doc arrived in 1931. Their actions in 1931 inadvertently altered 1986, erasing Doc and Einstien in the process as well. Their actions in 1931 also alter ALL the years after 1931, including 1955 (which explains why George and Lorraine have reverted to their 'Twin Pines' incarnations). Fair enough.
But WHY would a divergence created in 1931, alter 1885, a point in time which PRECEDES the divergence? In other words, why would the ripple effect, which usually movesforward in time and changes the future, suddenly move backward in time and change the past? It doesn't make sense.
If we go by the evidence of the game, then logically, when young Emmett hooks up with Edna, 1931 Hill Valley would spontaneously start transforming! The name of the ravine would suddenly change from Eastwood Ravine to Clayton Ravine, Doc's letter with the Western Union would disappear as would the Delorean buried in the Delgado Mine, the pictures of Doc (and Marty) by the newly constructed clocktower, taken in 1885, should also disappear from the book in the library...without anyone noticing anything!
It makes sense for photographs and newspapers from 1986 to start changing, because these objects represent the future, which is not written...but why would objects from the PAST change?