I think asking someone if they can still reproduce an issue is valid. Especially if it was trivially reproducible for them, and now it isn't, that seems like a fine resolution, and the bug should be closed.

But in the other cases, closing the bug seems to me to be a way to perturb metrics. It might be true that you'll never fix a given bug, but shouldn't there be a record of the "known defects", or "errata" as some call them?

For your specific scenarios:

- lack of information on how to reproduce or resolve a bug doesn't mean it doesn't exist, just that it's not well understood.

- For the "new version" claim, I've seen literal complete rewrites contain the same defects as the previous version. IMHO the author of the new version needs to confirm that the bug is fixed (and how/why it was fixed)

- I agree there are high cost bugs that nobody has resources to fix, but again, that doesn't mean they don't exist (important for errata)

- Similarly with proprietary data, if you aren't allowed to access it, but it still triggers the bug, then the defect exists

In general my philosophy is to treat the existence of open bugs as the authoritative record of known issues. Yes, some of them will never be solved. But having them in the record is important in and of itself.