Ooh my people!
One thing that bugged me, in the books.
In Deathly Hallows, Fenrir insinuates that he doesn't have a dark mark to summon Voldemort with (in the Malfoys manor)
But, in the Half Blood Prince, Draco created that 'magic line' where only Death Eaters with the Dark Mark can get up to the tower where Dumbledore is and Fenrir was there!
ETA - I'm watching Prisoner of Azkaban as I type
Just my bit of crazy internet person @deku, it's not just you!