Continuity mistake: In the beginning after the car chase, the helicopter spotlight that follows Blade when he runs away from the man he just killed is much different than in the video on the computer that the female vampire is watching.
Continuity mistake: When Ryan Reynolds falls into the room he was chained up in after he gets scared by the vampire dogs, he hits the bar above and bends it. However, when he runs over to Blade after he has just defeated Dracula, you can get a perfect view of a now perfectly straight bar.
Continuity mistake: When King tells Danica that her hair is ridiculous, she touches the hair above her head. The shot changes and she's now touching the sides of her head.
Continuity mistake: When Blade speaks with Dracula at the top of the building the sun changes in every shot.
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.
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.