What are the chances that you'll be fired? And how will this affect your future career advancement at this company?
If you think you'll be fired, or your future advancement will be stymied, then is it possible to line up another job at a different company, and then resign before the mistake is detected? If you get a different job and then resign, then you're an ambitious go-getter.
If you get fired, you'll have to tell this story again and again... and, by the way, it's a story that makes you look careless and sloppy, which is not a great look for a data analyst type of position. Optics matter to your professional career. Make sure you consider them.
Don't know about being fired unless the external party makes a big stink. I work in an extremely niche field and it's a two-person team. So if I get sacked, then the team doesn't function for awhile.
Keeping mum could work out--since the report is over a year old and no one noticed anything. But if anyone just took a cursory look, they could see things not adding up and the consequences would be dire. So coming clean really is the only way to go. As advised by many, I will have to step up and offer solutions.
I cannot feign ignorance because the request to go back for additional data would blow away any chance to say I didn't notice the mistake. Actually, funny enough, the only way I can do it is to work with the faulty data and submit even more of it. I only discovered the mistake because I used another process to find additional data and that's how I discovered the problem. Otherwise, if I had worked with the data in the same manner as the original, I wouldn't have noticed anything. So I guess I could go that route...
I don't want to chance it though. The fact that the external partner is being repped by a new person--he may not overlook things as much as the previous rep. The latter didn't question anything. Maybe if he had, the problem would have been nipped in the bud early. Now, we're 1.5 year after the fact and submitted many reports since then. So the ripple effect is also a huge worry and a mess to untangle.
Finally, just wanted to clarify that while the data is wrong, we have not invoiced for any more than we produced. We have more than enough to warrant full earnings--just the data is jumbled up.