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That comparison would be a bit hazy due to boundary changes for many constituencies.
Yup, but you can (and everyone has been) infer around these. Imperfect but the best we've got.
On the former point my understanding is that the evidence is Labour giving up/sacrificing vote share in safe seats (i.e. decreasing) in favour of focusing on converting seats.
I'm not sure there's evidence of that as much as reporting of that having been the plan. Whether the plan worked in practise (or the vote was just split between Tory/Reform in those seats) is what I want to see. I'm sure we'll see that both will have happened, tbf.
If there is evidence/analysis on this please link!
But key to this would be setting it against voter turnout. Which I'm not sure how you'd do.
I'm not sure about this. Voter turnout is voter behaviour. Not turning up is a vote for something in a sense. You could think of it as the equivalent of voting for a third-party in FPTP (assuming it's not down to an external factor like IDs).
There's definitely more interesting stuff you could do with it (where was it? was it in areas that were historically tory? labour? etc.), but those are different questions.
That comparison would be a bit hazy due to boundary changes for many constituencies.