I think you got it. Reprints are often changed (re-inked or updated) for various reasons, so even though the story is the same, the reprint could be different enough to warrant its own copyright. And even if it's identical down to the cover and the ads, the renewal still gives Harvey the right to file a DMCA request or sue. Even if they lose the case in the end (I don't know the UK's rules, but the US requires the loser to pay the winner's legal fees in copyright cases so that there's no long-term economic downside to suing or being sued as long as you're in the right), who wants to put Serj through that mess just for a reprint?
Again, the IW reprints are almost always OK, because Waldmann used the printing plates as-is and didn't file for copyright. Microfiche collections are fair game, because they're just pictures of the out-of-copyright book (though the collection itself could carry a copyright for the presentation). Any other reprints definitely need a case-by-case check, and I think we'd all be happier erring on the safe side and just trusting that copyright registrations are valid if they're in the system.
