Once you sign a record, it is locked. You can update it, but it will have a second entry with a different date/time stamp. You cannot (easily) get into the databases to change this. This should hold up in a court of law, but then ...
Sometimes, this is cumbersome, since you might have forgotten to add something, or at the end there is a "Oh, by the way..." But I'm sure it was done for that very reason.
