No, this is not ok and it will only count as voluntary prayers for them.

I have seen some people attending second congregational prayer though they have already attended the first one in the same mosque. The reason they say, is that they have missed some congregational prayers in their life earlier and hence they are attending the second one, though they have already attended the first congregational prayer with the Imaam. Is this OK? Is this permissible? I hope you have understood my question.