Vic says Angela "thinks there are five of you" -- Beth, Katja, Sarah, Alison and probably Helena. Donnie replies that there are eleven, but at this point we know of twelve clones: those five plus Cosima, Danielle, Arianna, Janika, Rachel, Jennifer and Tony. Possibly Alison, in telling Donnie, miscounted those previously killed; or omitted Jennifer (who died of genetic disease) to avoid making him worry; or omitted Tony because she has not accepted his strangeness.