I agree with Zexion, reading based on discards is bad for multiple reasons, it's best to, at most, use them to decide who you want to pressure, but they should not influence reads.
However, even then I think it's better to not even use them then, 3 scum cards is possible (And of course, 2 is more likely than that, which you could still use to pick one for alignment and one to discard), so it's best to not really work on them. This leads to WIFOM of "But maybe he discarded a scum card on purpose because it lowers suspicion" and other such thought processes, which get us nowhere, as we don't know what cards people got.