Define provenance/pedigree? For example, I'm about to buy an 1806 halfpenny from Michael Gouby. I asked him about provenance and he said all he could remember was that he bought it from Spink at a coin fair. So there's no evidence that it was ever in an 'important collection', but frankly the two names of Spink and Michael Gouby gives me confidence in the coin. Would I have paid extra? Perhaps just a little bit, but it's not that important.
I've not heard of any - the first proofs were the 1971 set. I think those were struck in the early 70s at the London Mint who were too busy before 1971 to bother with proofs.
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Footnote:
I've just entered values for George VI and almost across the board those prices have increased. It seems his reign has been undervalued and is now catching up. (Mind you, mostly there are only values for EF and UNC - but to compare, Elizabeth II is static.)