That question, a crucial one, still has not been answered by the IRS. The best I can get from them is that they will take each case on an individual basis.
I interpret that to mean that if they feel the error is grievous, they will sock the taxpayer. If it's a minor miscalculation, they will be lenient.
In truth, the law, as it is written, does not permit late recharacterizations. I think that Congress may have to get involved, via a law change.