I wonder about that. Angelus never killing a slayer. He said he avoided them, he never did say whether he hadn't killed one. Think about it, if Angelus had been known to kill a slayer he would've been at the top of the Council's list to be killed, at least, even more so than he was. Spike, however, is always the bragger, never caring about who knows or not. Actually, caring about who knows about his exploits.

A demon like Angelus, one of the most vicious vampires the Council had known, would've killed a slayer or two in his time. If not, then he was being careful, feeling free to carry on decimating Europe without too much interference from the Council. ;0)

On the other hand, wouldn't the Council have sent Slayers against Angelus because he was such a monster?