Ingrid has spent the time between the second and third series - four years - "making the streets of Stokely run red with blood". Not only is that a fairly horrific number of attacks, but just imagine what things would have like for the rest of the characters, mindwiped by Vlad... if they were anything like Renfield, they wouldn't have been able to quite grasp what was obviously happening around them.
Elements of this have been somewhat confirmed... Eric van Helsing was killed by a vampire after he passed out while facing them thanks to the mindwipe.
Ingrid's 'hit chicks' and their deaths - on the one hand, yes, they're vampires... but they were ordinary human teenage girls only hours before, and they didn't even particularly want to kill Vlad! The more you think about it, they're kind of tragic.
Some survived, and S 4 E 1 revealed that a half-fang's loyalty to their maker doesn't last long (as Ryan turns against Ingrid), meaning that we've now got an army of teenage Vampires walking through Garside).
When Vlad opens the book the pages are blank but Vlad tells the others that their time had come like there was something written on them. But maybe there is writing on them, only Vampires can read it!
Or only Vlad can read it. Or they really are blank and Vlad's good side thinks he can use it as a chance to put his plan for vampires and breathers to live together by making out he's the only one who can read it and saying that's what the books says.
May have been Jossed. Vlad seems to have confirmed the pages really are blank.
Wolfie ages in dog years or close enough. Just look at him, in series 3 he looks more like a 6 or 7 year old and not a 4 year old, and in series 4 he looks 8 or 9 years old.
When Vlad said he couldn't mind wipe someone you care about to explain why Johnno wasn't mind wiped in S 4 E 10 must mean Robin wasn't mind wiped at the end of season 2!
It's also likely that Vlad was just telling himself that. After all, Jonno was mindwiped at the end of Season 2, and we saw the Branaghs (whom Vlad definitely cared about) were mindwiped.