Sirius found out after his brother Regulus died that he was killed by Voldemort or Death Eaters because he's had a change of heart and tried to stop being a Death Eater or refused to carry out Voldemort's orders. When we find out what actually happened to Regulus, it seems like Voldemort would never have known about his change of heart. Unless he was trying to do damage control by putting out that he'd had Regulus killed because he vanished without a trace and no one wants to think a powerful wizard could mislay a supporter. We know that Voldemort never knew Regulus had stolen the locket. The only thing he knew for sure was that after Kreature had helped him, Regulus disappeared. I can believe that because of the Death Eater tattoo, Voldemort would have known he was dead, there being no one on the other end of the Regulus communicator, as it were. But as to the why and where, clearly that was unknown or Voldemort would have shifted himself to find the locket soonest.
Booklists for year 7. Did Harry, Ron, and Hermione get their booklists? Normally, owls can find their owners to deliver letters, but presumably they didn't arrive until after the wedding. For Ron, they probably would have delivered to the Burrow, but they had no problem finding Harry in the Cottage on the Sea (although it arrived with Hagrid) so why would they not be able to deliver to Harry wherever he was? Or Hermione wherever she was. Come to that, why can't they detect that Ron isn't at home? Owls find Sirius (eventually) who is on the run, so wouldn't they be able to test whether Ron is home by sending him an owl, and seeing where it goes?
Edited to add:
Hermione says when they're in the tea shop having just defeated the two Death Eaters after escaping the wedding that she's never done memory charms, but understands the theory. How did she modify her parents memories if she's never done memory charms? What did she do instead? I think that's an editing/continuity error, personally. Bad editor! Bad!
Is SPT's prophesy in Prisoner of Azkaban to HJP in the Hall of Prophecy (I mean, before the kids smashed up the room) and how it is marked? I got the impression that things got in the hall of prophesy by being sort of Pensively extracted and captured in a crystal ball and collected, but what if it was a more automated process? Magic is detectable, and therefore so could prophecy. But clearly it doesn't solve its own riddles as evidenced by the label on the STP/APWBD prophecy in which Harry's name was written in later, after being attacked by Voldemort. So if it was an automated process where the prophecy just appears when uttered, it should appear like this, "SPT to HJP. Dark Lord and Sirius Black. If it survived the night at ministry, it should have been relabeled, "SPT to HJP. Dark Lord and Peter Pettigrew." It doesn't make sense, in my opinion, that Dumbledore would be able to report on the prophecy since he didn't directly hear it. So if a prophecy happens and no one knows to report it to the ministry, did it happen?
Edited to add:
Peter Pettigrew/Sirius Black/Death Eaters. I can understand why the DE have no particular interest in clearing the air on the Sirius Black vs Peter Pettigrew, "who is the traitor," issue. It's surprising to me that Karkaoff doesn't try to throw the blame to Peter Pettigrew during his trial, but on the other hand, why would the ministry pay off for dead Death Eater and it seemed like everyone, including Black, believed Black killed Pettigrew. Karkaoff says that V tried to keep his Death Eaters away from each other, but yet Black says earlier that the imprisoned Death Eaters in Azakaban blame Pettigrew for Voldemort's downfall. How did they know who to blame? I guess I understand that Bellatrix would know Sirius was more likely to be Order of the Phoenix than Voldemort, and possibly even who the traitor was, but it seems like if it's common knowledge within Azkaban, how did the Ministry of Magic and Dumbledore NEVER hear about it? I can understand the Dementors not caring, but it seems like some of the prisoners might have mentioned at some point.
My other question is the DE tattoo. It seems like the Ministry would find a way to make the tattoo show itself so they could confirm who is DE and who isn't. Also, it seems like, from Draco's experience in Madam Malkin's, that the tattoo is visible all the time. Otherwise, why would he feel the need to conceal his arm? Possibly it's a new tattoo so it takes time to fade into the skin? Maybe? But it seems like as long as V is strong, it displays.
I think that might be all for now.