Defects happen but good manufacturing practices and QC checks should catch most of them. If there is a defective one in a lot, I'll get it... And indeed this happened with one of my three Totos. I had one tank that was slightly askew. I noticed while trying to align it within a gnat's a##...it looked different depending on which side of the toilet I was comparing. The problem became apparent when I put the matched lid (I didn't mix it with the others.) There was 1/8" or so gap on the corner and some tank twist was apparent; I also noted the tank walls were closer together on one side than the other. Functionally the toilet and tank were fine and I used it for several days before swapping the tank at the supply house. This was a substantial cosmetic defect and the tank lid wobble was unacceptable to me. I doubt 80% of homeowners/installers even would have noticed it.
Haven't needed a plunger so far...I'm waiting for a year plunger free to declare victory.