Something else to consider, too:
The LBT series is Not known for its detailed or even specifically Accurate storytelling and recollections of previous events. The earlier films (1 through 4 especially) were able to keep a good level of consistancy in character and story, I thought, and I have no issues with how they were done.
LBT 4: All we know of Ali is that she is in a migrating herd who recently came from the Land of Mists. Later on, we learn that she spent all of her social life with longnecks, which adds more detail. Still, her background is quite sketchy.
LBT 6: The story of the Lone Dinosaur is told in some level of detail, through the opening's story and the song "Lone Dinosaur" (most of which in the song is fiction, but that's besides the point). Overall, the story of the Lone Dinosaur is one of the better-developed historical stories in the series, and it is
Meant to be sketchy for the sake of mystery. Ironic, isn't it?

:
In LBT 7, there is a well-known discussion between the Gang about who crosses the vine first (when chasing after Pterano's posse). A comment is made that Cera is always at the back of the line whenever the Gang had left the Great Valley previously, yet in earlier films, we clearly see that Cera has never Once been at the back of the line when crossing any sort of gap.
Also in LBT 7, when the gang finds Ducky in the cave. The story of how ducky got there was kept extremely short (under 10 seconds). While this isn't as important of a story as Bron's, I believe this trend continues in LBT 10's Bron story.
LBT 8: Thicknose's story, told in his song. Most of the song is about the theme of never being too old to learn. A few seconds of the song tells the story of his life, but this detail is kept Very minimal. The story of where the Spiketails came from is also kept very sketchy. All we really know is they are from "The cold lands", likely on a more polar point on Earth than the Great Valley but possibly a mountainous area (though the lack of food in mountainous regions would suggest against that). Anyways, that's a different topic altogether.
LBT 9: The background of where Mo came from is kept very simple. We know nothing of his family except from what we see of how they act around him at the end. The story of how he got to the Great valley was kept very short and simple.
LBT 10: One of the most major, important backstories in the entire series is told in a matter of a couple of minutes, which is certainly possible
if the most Relavent information is given to the audience.My point? I have a couple.
If the previous sequels were so skimpy on details, why should LBT 10 be any exception? I believe that the important parts were left out and the parts that we hear are mis-interpretted to mean something outside of the original context of what truly happened. I understand that a children's movie will naturally have less detail offered to the audience than a more mature film but I think a story can be basic while still being well-done.
I think that the wrong parts of the story were told to the audience in the wrong way, and I think that Darkhououmon has some very good points.
Bron says that he couldn't find Littlefoot but there could be any number of reasons for that. Bron could have fallen ill or become disoriented in the sudden change of the landscape (or for some other unexpected reason). The change of seasons could have changed the position of the Sun and the stars, thereby throwing off Bron's navigation.
Some details were left out of the story that could have explained what Bron was Truly saying. Remember that Bron was talking to a child, and probaby was light the details for a number of reasons. Perhaps something horrible happened during his search that he didn't want to tell his son until perhaps he was older.
Why did Bron leave his wife when they had a perfectly good place to live?
Perhaps the area was becoming overpopulated or there was a wave of poor living conditions moving in their direction.
Why didn't she come with him?
Perhaps she wasn't in good condition to travel or couldn't move her eggs without fear of breaking them. Maybe some were broken in the process of trying to bring her with them and a single egg survived. At that point, I can certainly see her wanting to stay behind.
Why didn't Bron check the most obvious place, the Great Valley?
Consider the directions given to Littlefoot on how to Find the Great Valley:
Follow the Bright circle (where it touches the ground) past the rock that looks like a longneck and past the mountains that burn.
On Earth, the sun touches the horizon in two places: one in the west, one in the east. If Bron had simply followed the morning sun instead of the evening sun, he could have ended up in the completely wrong part of the world. Maybe Bron simply couldn't Find the great valley for a reason as simple as this.
How to find the Great Valley is on a topic completely different from this one (maybe I will start a topic on that) so I will stop there. I sincerely think this story is explainable but we just lack a large amount of information.
thoughts?