Theory throwing time!
Caveat: the narrator I’m following is definitely totally and absolutely reliable. It’s this one:
“I have been assigned to this sector by my superiors to find evidence of abandoned alien technology similar to that found by our competitor, the Atlas company, in the ruins on Prometheus; technology that many believe made them the superpower they are now. This kind of find seems astronomically improbable on a rock like this, but my benefactors believe in it enough to waste my considerable talents.”
- Tannis, Hidden Journal: Day 1
This supports what @swk3000 wrote. DAHL went to Pandora hoping for a find like Atlas had on Prometheus. Dahl did neither know for sure that there was a Vault, nor did they follow Atlas to Pandora. For now, nothing indicates Atlas coming first.
“When I attach scientific inquiry to something like the Vault, I am greeted with silly nursery rhymes and slack-jawed soliloquy about a man who knew a man who knew a man.”
- Tannis, Hidden Journals, Day 43
Obviously there were rumours about a Vault, but those seem to be as precise and convincing as the story of the jumbug in TPS. But this might explain why whole villages knew nothing about Vaults: simply because the Vault was a myth or a rumour not worth investigation.
“And then I noticed the emissive glow on the rocks at the dig site…”
Tannis, Hidden Journals, Day 76
“With the investigation of the symbols and glowing patterns at the site we have finally unearthed arguably certifiable proof of the existence of alien life having been here on Pandora.”
Tannis, Hidden Journals, Day 119
Alien life: Yes., proof of a Vault: uhm, still none, but hopes may rise.
“Two days ago, I explained to my mother how the translation program I was writing would greatly help me understand exactly what all this Eridian text I’ve attempted to decipher actually means.”
Tannis, Hidden Journals, Day 321
“Day 481. It’s true. It’s all true. My program did it. Program. Program… I am now certain that the Vault is here, and that the symbol has something to do with opening it!”
Tannis, Hidden Journals, Day 481
Between Days 119 and 481 we go from yep alien life to The Vault is Real and it’s here! And Atlas showed up, because:
(Parallel reading) “So, the Dahl miners found it difficult to get the Eridium off-planet, and soon found themselves wrestling with the Atlas corporation as they fought over the same resources. As it turns out, word of a Vault can travel many galaxies.”
“As it turns out, Dahl turned tail when the Crimson Lance showed up and flexed their various muscles. The central issue being that Dahl brought many workers here, including myself, and left without evacuating most of us. The bandits you fight out there used to be family men, workers, scientists… We’re all broken because of them.”
Tannis, Minecart Mischief transcript
We know when Dahl did “turn tail” from this:
“Day 493. Dahl Corporation just shut down their mining operations here on Pandora. I think they are insane. Or, that is, whoever is making the decision is insane.”
Tannis, Hidden Journals, Day 493
“Day 616. Sometimes, I wish I had never been given this assignment, and never come to Pandora. Dahl has asked me to leave. The transmission said it’s time to go. Everyone has left - except the criminals who they’ve let loose.”
Tannis, Hidden Journals, Day 616
And one more for good measure:
“The people that inhabit this salted dustball are as ignorant as I’ve seen in this galaxy.”
Tannis, Hidden Journals, Day 43
Some deductions from all that:
- Pandora had human settlements before Dahl went there.
- Dahl went to Pandora hoping for alien tech, without reliable knowledge there would be a Vault. Aside: it’s open for discussion if Pandora was the only frontier world Dahl sent science teams to. As can be seen from Axton’s story they are active on enough worlds.
- Dahl was there before Atlas. The Dahl miners had trouble getting the Eridium off-planet and soon found themselves wrestling with the Atlas corporation. Is it confirmed in any way that Atlas came for the Vault and not for this exciting new resource Eridium?
Anyway that still supports that Atlas came second and disrupted Dahl’s mining operations, leading to Dahl “turning tail” on Day 493. Dahl leaving Pandora was done around Day 616 of Tannis’ journal, still a while before the Vault Hunters arrive.
- Atlas kicked Dahl off the planet. Dahl tried to evacuate some key personnel (Day 616) and left the rest, including Zarpedon on Elpis and Hector in his mine. Meanwhile Hyperion observed.
- At some point Atlas left Pandora and Hyperion moved in. Correct me if I am wrong, but there are no stories of Hyperion winning an epic battle against Atlas. As seems to usual for Megacompanies in this universe, they abandoned part of their troops, which in turn resorted to banditry.
- Lots of the abandoned Dahl miners, scientists etc. turned Psycho or Bandit (Minecart Mischief).
- Since there is no society or frontier society without criminals, there would have been bandits anyway, but maybe not such numbers of them. So Dahl is responsible for lots of the bandits on Pandora.
There are lots of contradictions left. If Dahl had such a lucrative mining operation going on, why didn’t Atlas just take over? Who sailed the Wurmwater or Deep Fathoms seas as @1sirus2 pointed out? If there were humans for at least over 200 years, why did the last opening of the Vault go unnoticed?