Ending S being the "best" ending vs. Ending A being the canon ending in the main game. The game is played from Chuck Green's POV, what with him being the main character, and ending S is the only ending in which he, Stacey, and Katey all get to go home together. So it only makes sense that this would be the best ending. However, in the process of making this happen he is forced to grab and retrieve a bunch of Phenotrans items lying around, which could mean the amount of evidence against them is reduced by some significant amount, in order to save the girls from the massively Ungrateful Bastard he saved from turning into a zombie. Ending S essentially requires that you bury a vital plot point for future installments of the series to expand on by letting Phenotrans get away with their crimes in order to give Chuck Greene his happy ending. Ending A, on the other hand, doesn't give Chuck his happy ending with Katey and Stacey. However, it's still a good ending, as the two girls escape safely. Furthermore, it becomes the lead-up to Case West, where Chuck ends up teaming with Frank West to gather significant evidence against Phenotrans, in the process discovering very real possibility of a lifelong/permanent cure for zombification as well as its link to the high heel face turnedSpicy Latina from the first Dead Rising. Not to mention Marian Mallon's threat of another harvest, which ranks under possible foreshadowing for Dead Rising 3. In essence, Ending S may be the ideal outcome for Chuck on a personal level, but it quietly lets the story recede, whereas Ending A plus Case West fundamentally continues the story.
On the other hand, Off the Record has no Ending A. However, that doesn't mean there's no outcome where Phenotrans gets exposed for their evil deeds anyway. OTR's Overtime mode items have no concern with Phenotrans' cover, with the exception of that incriminating photo of the CEO having some fun at the Americana Casino. The rest of the items split focus between tokens to the Final Boss's affluent lifestyle and medicine to keep Rebecca alive after the gunshot wound she suffered at the hands of Agent S. Furthermore, more emphasis is put on the Zombrex stash within the gift basket item. This, combined with several hints from the 72-hour storyline, namely the leaked footage of the CURE activist starting the outbreak never being a part of the plan this time and The Mole outright claiming to have never dealt with him directly, whereas in the original game it was clearly the opposite, hints that the boss doesn't give two shits about covering for Phenotrans or getting back in good with them. Furthermore, with Frank West's photography in addition to Rebecca's videos, the heroes likely have much more evidence on their hands out of Fortune City about what really went down. Thus, Ending S in Off the Record is truly the best ending.
The fact that some survivors are more concerned with things like poker games than the zombie apocalypse? It's done on purpose to make a statement about the mindless conformity and consumerism of modern life. Everyone who is a zombie in the game was already a zombie without the virus. When they were alive they were just a bunch of faces in the crowd, mindlessly consuming. It gets even more brilliant when you realize that the game takes place in a transparent in-universe stand-in for Las Vegas completely made up of shopping malls and casinos, the ultimate symbols of conformity and consumerism. Blogger Charles Phipps expands on this beautifully here.
The Emergency Shelter not having Zombrex in it, Despite it being built in case of an outbreak seems like a dumb oversight on the planning departments part, even in Dead Rising 3, the mortuaries have emergency Zombrex, just in case, then it hit me, The emergency shelter did have Zombrex, but Sullivan/Stacy (Depending on the game) either disposed of it, or stashed it away just in case they got bit, after all the plan was to have every survivor bar them killed and escape on their own, so letting in infected survivors and letting them turn was one of the methods they were able to use, except Chuck/Frank was more forward thinking in going out and getting some, preventing that plan.
Katie's headphones. At first, it seems likely that they're connected to her game system. But she's always wearing them, even when she's asleep. Katie is a trauma victim, so the headphones might be there to cut down on potentially triggering noises.
TK's perverted comments regarding Stacey or Rebecca in the phone call that kicks off Overtime Mode go beyond admiring the woman's beauty. He outright implies that he raped her. It's even worse in Rebecca's case, as between his intention to keep her alive and the fact that one of the items he wants Frank to get for him is a pink silk speedo, he seems to be intent on her becoming his new sexpot.
In the Case West DLC, there is an Underground Tunnel where there is sounds of a woman crying either somewhere in the Tunnel or at least somewhere near the Tunnel. Did she survive the facility, or was she killed in the end? For added horror in regards to the ending of Case West, if she was killed, was she killed in the explosion, or did the Zombies or Phenotrans Goons get to her?
Around that area, there is graffiti that says, "Don't startle the witch", an obvious reference to Left 4 Dead and it's own Witch zombie. Why is there a Witch in the Dead Rising universe? Are Phenotrans experimenting with other sorts of mutated zombies? And imagine how much more dangerous a Witch would be in Dead Rising, since the higher zombie density would make them a lot harder to spot.
The obvious and oft-mentioned requirement of Chuck being present whenever he administers Zombrex to Katey. Especially galling when the first survivor you're ever likely to save works at a pharmacy and is probably capable of working a syringe. Chuck may not like having to rely on a stranger to treat his daughter, but that's both something adults literally do every time they take their kids to the doctor and far less risky than leaving her alone with transparently unhinged and selfish survivors for hours at a time.
It might be because some of the survivors are unhinged and selfish that Chuck gives Katey the Zombrex himself and keeps it on him. He's tough and the survivors wouldn't be that dumb to pick a fight with a guy that can exterminate zombies by the dozens, something they've most likely seen firsthand. But if he left the Zombrex there, there's a fair chance it'll be lost whether by theft or accidentally destroyed as the only line of defense is Stacey, and some people wouldn't have a problem leaving a little girl to die with their life at stake. There is Sullivan as security, but considering he's the mole, there's a good chance he might turn a blind eye.
Or, it might just be the case that Katey only trusts her father to give her the injection, not a stranger she's just met. It's also a matter of not telling anyone that she needs Zombrex. In the story, Sullivan only let her and Chuck stay in the bunker because Chuck told him he had Zombrex for her. If he, Sullivan, or Stacey told all the panicked survivors that there's an infected survivor among them and no Zombrex around, they'd be very paranoid and desperate to kick her out before she turns.