I've been noticing a decrease in quality control from Lego lately or I'm also having bad luck.
My NES set isn't fully built yet but bag 1 had an incorrect swapped piece. Fortunately it was a common piece so i just went into my spare bins and pulled out a dark grey wedge but this is the 3rd set recently where something similar has happened. Also instruction book 1 had some kind of....gunk inside it smeared all over one page and soaking through about a dozen pages on each end. Oily nastiness. It did not affect being able to follow the instructions but ruins the nice manual.
I don't know if this is common or if I just have the worst luck, but I've had an issue with every large set I've owned. Looks like I'm missing a small bag of parts in the NES set this time. Yay.