Why did my disposable camera not give me the number of exposures advertised?

I haven't used a film camera in a long time, but I recently used a disposable camera I got from Walmart to take some photos. The camera's box said the camera had 27 exposures, but when I got the photos developed (at Walgreens), I only got 19 prints back. That's a whole eight photos I took gone missing! Is this normal for a disposable film camera?