No, I mean I think I may have seen the same thing in some earlier time-travel show or movie, where an anachronistic underwire bra was useful for picking a lock in the past. I could just be having deja vu, though. Maybe it was just the underwire-lockpick part without the time travel -- but it sure as hell wasn't in Friends, a show I never watched.
Well, from any POV that really makes sense, there's no danger of your timeline being changed at all. Real physics allows for only two possibilities: the self-consistent or post-selection model, where any time travel to the past is simply part of the one and only timeline and was always part of the events that cause it to unfold the way it did, and the probabilistic model, where the time travel branches off a parallel history that coexists alongside the unaltered original. Both mathematically and logically, the premise that an event can happen and then be made to have not happened is absurd and meaningless. Any timeline that exists will always exist; at most, an alternate can be created alongside it.
So any work of time-travel fiction that allows for the original timeline to be "rewritten" at all is more fantasy than science fiction, and so the rules can be fairly arbitrary. Still, the important thing in fantasy is that the ground rules at least be self-consistent. I suppose the "San Dimas Time" model could sort of be justified if you assume it's a property of the two time machines being linked -- maybe that link requires the two machines' internal clocks to remain synchronized, so that anything that takes X hours in the reference frame of the main machine will also take X hours in the reference frame of the "lifeboat," no matter how far apart they are in time.
Well, yes and no. As stated, their mission is not to preserve the original timeline per se, but to prevent Flynn from unmaking the United States of America. As long as the US and its values continue to endure, then the mission is successful even if a few details of individual lives are modified.
It's actually a bit like an earlier NBC time-travel show, Quantum Leap. There, Sam's "mission" was specifically to change history in small-scale ways, to alter individual people's lives for the better, and it was occasionally theorized (at least in the tie-in novels) that the ultimate end goal of this was to create a better future overall. The show focused on Sam's end of the story and rarely showed the changes his actions caused uptime, but the novels by Ashley McConnell often addressed how the timeline was constantly shifting around the folks up at Project Quantum Leap. This is in a similar vein, although it's also an opposite one, since the heroes' mission is to prevent or minimize changes rather than causing them.
That's because "undoing screwups" isn't even on the table. The "no backsies" rule ensures that. Flynn's actions are what dictate the sequence of events. He chooses where to take the main time capsule, and the lifeboat can only lock onto wherever the main capsule is and follow it there. So the only thing the heroes have the option to do is to react to Flynn's sorties into the past and try to head off his attacks on history -- ideally to prevent any change at all, or at worst to minimize the impact of any changes they can't avoid.
As for Flynn, it seems the most logical option for him would've been to start much further back than the Hindenburg. If he really wants to unmake America, as they believe, why not go back to the late 1770s and give modern weapons to the British? But maybe we don't know his real agenda yet. Although it does seem that he's trying to follow the book Lucy will write in the future, so I expect a degree of causal loopiness.
Actually, the larger the interval between generations, the less likely it is that the death of an ancestor will prevent a descendant from being born. Humans have a finite number of chromosomes, so beyond maybe 8-12 generations back, the odds that you have any genes at all inherited from a single given ancestor fall toward zero. For instance, 10 generations back you have 1024 ancestors, so if one of them is killed off, you still have 1023 other ancestors whose descendants would be able to contribute to your eventual existence. And the one ancestor who's removed could just be replaced by a different one, since their spouse would just marry someone else. And if it's far enough back that they would only be your geneological ancestors rather than genetic ones, then that substitution might have zero effect on your own genes. If the right distant ancestor were removed at the right point, then the cumulative effect might amplify and erase your whole family, but it's more likely that the loss of that ancestor's contribution would be damped out by the contributions of all your other ancestors from that generation. It may seem paradoxical, but removing a given person from history would probably have a greater effect on their immediate descendants than their more distant ones.
but like you said, their mission was intentionally the opposite. Sam didn't care what happened to his 'original' timeline (despite the tagline about hoping his next leap takes him home). His actions were intentionally making changes, so he was never going to return to what he would consider home, it would be drastically different. Was there ever much description about what was really going on in his present? Entire mission only makes sense if something has gone somewhat horribly wrong, but don't recall that being the case. Al seemed to be having a somewhat normal life, so messing with the timeline on that scale seems odd.
