Eh, that isn't really a continuity issue, it's just we the audience don't know the whole story. We don't know when Icheb joined. When Seven wanted to...
It's all good though, because ATLEAST the movie will really honor Chad. After all, it's all about him and his legacy... Ignore how pitiful and trash...
I mean at this point who cares? They already made their choice, they gutted the male cast, over stacked the female cast, completely wrote themselves...