Revealing mistake: While Blade's dangling a familiar off the roof, the familiar's phone rings (a Nokia 5210). Blade looks at the screen and sees the doctor's name. However, the display we see is a Nokia phone book listing with only one entry, rather than the "incoming call" display.
Revealing mistake: In the very last shot where Blade is seen on a real tight shot and then it pulls out to reveal him on his motorcycle, that is obviously not Wesley Snipes. The skin was lighter, and as it pulls away, you see the side of the face for a moment, and it sure ain't Wesley.
Revealing mistake: When Dracula is on the autopsy table, disguised as Blade, he can be seen taking a breath (look near the neck).
Revealing mistake: In the scene where Blade kicks Triple H and he goes through the wall, you can see the hole in the wall before he flies through it.
Revealing mistake: At the beginning of the movie when the four guys are in the pyramid, one of them bends over and pulls out one of the stones it can easily be seen that the surrounding stones are not real as they bend upwards when the stone is pulled up.
Revealing mistake: When they find Abigail and Blade, Sommerfield is dead and suspended by nothing but wrist restraints above head level. Her arms are bent as if she were standing up. Her arms would be straight if she were dead, since her wrist restraints would be the only thing supporting her body weight. (01:21:08)
Revealing mistake: While Blade is in jail and is being rescued by the Night Stalkers, he is fighting Jarko. He kicks him through the wall. The wall begins to crumble before Jarko's back touches it. (00:33:15)
Revealing mistake: Throughout the final fight-scene, anytime Wesley Snipes' face is not on camera, you can often tell that Blade is played by a stunt-double. The double is a bit thinner than Snipes, which gives it away.
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.