Continuity mistake: When Blade speaks with Dracula at the top of the building the sun changes in every shot.
Continuity mistake: At the beginning of the movie when the four vampires are in the pyramid, the vampire with the scanner in one shot has his light stick across the scanner, in the following shot it is below and pointing down, then the shot after it is back up across the scanner. (00:03:15)
Continuity mistake: Just after Dr Vance has talked with Blade, he takes a needle out of a pack which is on a table on the left side of the room which you can see in the two way mirror, but in the following shot the two way mirror is behind him. (00:31:20)
Continuity mistake: Hannibal wears a "Hello my name is" tag that seems to slightly change condition and placement during the rescue of Blade from the familiars. Then when they get back to the Nightstalker lair, there's a close-up in which the tag looks nearly new.
Continuity mistake: The Daystar Arrow changes size between shots after Blade stabs Drake with it. When it is first fired by Abbigail, it looks to be about the size of a standard arrow (it looks at least 24" long if not longer), but when Blade later picks it up and stabs him with it, it suddenly shrinks in size quite a bit. In a few shots, including the tip, it looks less than a foot long. Only the tip is buried into Drake's chest as shown in the film, so that can't be an explanation. Also nothing in the movie indicates it might have snapped or broken. (Drake caught it and dropped it right before being stabbed with it, which shouldn't have broken it). It literally just suddenly is about half the size it was.
Continuity mistake: At the railway station, when Abigail Whistler begins to take out the first street punk with the silver knife from her boot, her hat comes off, but in all the following shots it is back on. (00:20:40)
Answer: It's possible that he followed one of them back to the base. This is feasible since they wouldn't be able to tell that he was following them because of his shape-shifting abilities.