At the outset of the novel, the Party isn't playing a fair game, in which people need to be persuaded and may choose to comply or not. The Party largely has won. Their aim is never, ever to inform. It is only to further subjugate.
There is one major misconception in the question: the Party does not want to minimize the conflict between peoples' memories and the current situation as it is described to them.
The point wasn't for the government's position to be plausible and convincing to most people, it was to extend the government's authoritarianism so completely that people would adjust their cognition to suit rather than question the government's message. That's exactly what doublethink is-- having access to information which must be literally correct while being able to not reject conflicting "official" information to any degree.
But more broadly the degree of effort required to update historical records isn't relevant. People need something to do with their time, lest their thoughts turn in directions the government doesn't want. It's also meaningful to the government that work not improve peoples' standards of living. A repetitive, dull task which can never really be completed suits those just fine. Plus, in that setting, who would even be rifling through historical records, and for what purpose?
It is also helpful to the government's aims to have historical information either not exist or be completely unreliable, and once again this mechanism helps. The news needs to be disseminated (the conditioning the government wants to instill needs regular messaging to individual people), and any physical medium for that (such as newspapers) can leave a record behind. Constant tampering with records makes that less impactful.
The government in 1984 is also explicitly engaged in efforts to destroy information in the human mind. And I don't mean eliminate inconvenient facts, I mean cause meaningful harm to the concept of epistemology.
The efforts towards Newspeak are the most blatant example of this I can think of offhand-- the effort is to debase language to the extent that many ideas cannot be expressed at all, let alone considered or transmitted between people. Making sources of knowledge about the world unreliable furthers that.
This is of a piece with the core government ministries having names which exactly contradict their purposes, and the government's mantras like "War is peace".
Consistency exists in some places, but it is more of habit and not any sort of consistency of information. The chess problems in the newspapers are a good example of this: white always wins, and black (whomever that may represent) always loses. In that sense, it simply doesn't matter which nation Oceania is at war with.
Finally, the consequence you imagine is not too much of a threat. The Party works, above all, to maintain itself in power. That is fundamentally what the Thought Police are for. The entire arc of the novel is an example of just how hard the Party works to root out and quell even the mildest stirrings of dissension, let alone meaningful rebellious action. The Party even maintains the idea of a specific, active rebel element as a further tool of social conditioning and neutralizing dissent.