21 is fixed for me.
For me as well. ##309 is still screwed up
309 is already confirmed, to late to fix anything

Hardly, slush has several times fixed bad blocks after-the-fact by adding revenues to other blocks in the confirmation chain.
This is not Slush fixing it. This is automatic. If error is big enough system finds it and fix it. I'm not sure but I think that if an error is less then 20-25% will not be fixed...