A "Tav" was written instead of a "Hei". The sofer before erasing the regel of the Taf put down something on the klaf to soak up the dio a little that it should be easier to erase. After doing so he saw that the "reish" part of the taf had also lost a bit of it's color and before erasing the regel re-wrote the reish part. Is this considered Nictav b'psul? Since that chelek was written b'kashrus, only the regel makes the ois pasul he only has to erase that. However now before erasing the regel he re-wrote the reish with the regel there in place. Maybe this is not called "Nictav b'psul"? There was seemingly enough dio still (and dark enough) that it would be considered Kosher. However maybe writing over it makes a problem now.
Any thoughts please share!