The Last Line Effect
I'm not convinced that this is necessarily caused by people losing attention while they write the last line due to anticipation of finishing the task.  Other possible theories I can think of:* People make mistakes in any line, but they often unconsciously review them and spot the mistake while they're writing the next line.  In the case of the last line there's no such automatic review.* (plausible in some of the examples, not all of them) The last line was added by copy–paste at a later date than all the others.