I was reading the NaNoWriMo main site yesterday (yes, book avoidance tactic no.483) and it points out that different computers have different word counts. If any of us should ever reach the 50k in the deadline, it must be the 50k on the NaNoWriMo word count - if you go on the site, it tells you how to check your current word count and see the margin of error.
NaNoWriMo site says:
It's November 25th, 2006. I've written 50,000 words and am ready to enter into the annals of NaNoWriMo history forever. How do I get the thing verified and have my name put on the Winner's Page?
From 12:00:01 am, November 25th onward, all participants who have written more than 50,000 words can have their winning word counts verified by our world-renowned team of robotic word counters.
Uploading your novel to the Validator makes your NaNoWriMo victory official, gets you listed on our Winners Page, and routes you to the secret spot where you can collect this year's winner's certificate.
It will also turn your word count bar purple and add a small celebratory banner to your Flash Profile.
The Word Count Validation tools are part of the My Novel page in the My NaNoWriMo section of the site.
What if there's a discrepancy between what my word count said and what yours comes up with?
Word counters rarely agree with each other, and there is a good chance there will be a discrepancy between our counter and the one on your word processor. Some people gain words and others lose them, and you can see how great the difference is by uploading your manuscript for counting at any point on the My Novel page. Our count will automatically appear in your Word Count box.
The link is http://www.nanowrimo.org/modules/xoopsfaq/index.php?cat_id=16#62