The most important words in your first paragraph are ‘should’ and ‘pretty close’!!
I find that the more intricate pieces within a block, the more likely the final product is neither a perfect square nor the right size. Small errors in cutting and sewing, stretching along a bias edge, and other variables are magnified the more seams are in there.
But I am NOT a perfectionist. I do the best I can, and try to learn from each mistake, and make a new mistake next time. My quilts are warm, cozy, and full of love, but will never win awards. I’m good with that.