Google Background Check

What does Google's background check actually entail? I don't have an offer or anything, but when I initially filled out my application, I wrote down employment dates purely from memory and now I'm realizing that some may be a bit off (by a month or so) and I just wrote down my best guess for the jobs I had more than 20 years ago because I just did not remember at all so those can possibly be off by months. Will this be an automatic deal breaker if/when they eventually do a background check? Any suggestions on how I should handle this?