My employer forgot that I took 3 days of annual leave - do I remind them or take the extra days?

We recently switched HR time booking systems at work. For some reason, the system knows that I took 3 days off in January, but it counts them as "0 days". I reckon someone messed up because all my other annual leave days show correctly. The thing is, my boss has very little oversight over who takes what holiday. The person who approves my holidays and the person I report to don't talk to each other much (think of a big corporate place where nobody knows who reports to whom). So *what I'm thinking* is that I don't alert them to the error and just take my extra 3 days sporadically (a Friday here, a Monday there). I'm fairly certain nobody is going to find out. What do you think? Yea or nay?