I've convinced myself that this happens in gmail / hangouts history search too. It'll very confidently tell you that here are the only six results for your search term going back to the beginning of time, but if you go and manually dig up something that you know is there from ten years ago, then all of a sudden there are seven results the next time you search for the same term.
I haven't done this methodically, and I can't prove that this is happening, but it's infuriating nonetheless.
I haven't done this methodically, and I can't prove that this is happening, but it's infuriating nonetheless.