Revealing mistake: In the opening scene, Novak attacks and bites a woman, and when the security guard begins to shoot at Novak there are bumps on Novak's back exactly where he gets shot, signifying the explosive squibs. (00:02:50)
Revealing mistake: This is during the fight between Blade and Nomak at the House of Pain. While Blade is walking across the wooden platform, you can see Nomak readying himself to get launched on the platform. (00:52:20)
Revealing mistake: When Blade slices Reinhardt in half, as the sunglasses fly off the two halves of his face you can briefly see that Reinhardt (or more precisely the CGI model of him) has no eyes. (01:37:23)
Revealing mistake: When Damoscinos is dying, just after being bitten, he stumbles to the ground. As he does so, you can see the tube feeding the green "blood" to his neck on the ground behind him.
Revealing mistake: Near the end, when Blade pierces Lomac's heart with the sword and blood comes out of his mouth, he starts wobbling around and they do a wide shot, behind Lomac you can see the tube that feeds the blood on the ground and it comes up under his costume.
Answer: In Blade I we saw that with sunscreen and the avoidance of direct exposure Deacon Frost and his lackeys could go out by day. The reapers are probably two or three times more sensitive than normal vampires so the exposure was probably not long or direct enough to kill the regular vampires.