Thanks for the purchase, and the questions!
The short answer is that the only information that players are actually required to treat as canonically accurate are the traits on your character sheet, and your successful alibis. Players can set up whatever information they want as part of the scenario - it can be as simple as "Guys! The last Hot Pocket is missing!" and then everyone runs in and starts yelling at each other, or as complex as "everyone agrees there was a Hot Pocket in the fridge at 11:30 PM last night, but when we got up at 8:00 AM and we were all gathering in the kitchen it was gone." But that doesn't actually have to be true - one player can, as part of an accusation, say, "Wait a minute, did anyone but you actually see the Hot Pocket after yesterday afternoon? Because I thought I saw you eating a Hot Pocket yesterday afternoon while you were watching wrestling."
If your alibi fails, it is entirely up to the other player how much of it they want to tear apart. However, much like traits, their counter-evidence doesn't actually become verified truth unless they incorporate it into their own alibis later. If they provide a timestamped photo, another player can absolutely accuse them of having photoshopped it as part of another accusation, and if they say the Hot Pocket is vegan someone could fish the box out to try and show that it has meat ingredients. If Player A claims to have been at Meat Is Murder, someone else can interrogate that fact, and A will have to defend it to get it as an alibi.
Generally, I assume that players are going to mostly want to tear down small sections of alibis rather than the entire thing, and will more or less treat statements as true-ish, but you can get as chaotic as you need to.
In terms of bonuses, my intent was that you only take a given +1 or -1 once, even if it could apply multiple times (although it could reduce how much of your alibi can be torn apart, since they can't contradict your traits in the process.) In the example, you still only get +1 for applying vegetarianism and your relationship, but on the other hand, your accusers can't say you broke up with your signficant other as part of their explanation.