I once backed an 85" square quilt with a center panel surrounded with a large mitered border in contrasting color. It was a clever and stylish way to use what was available in stash but sent me jumping around the living room in fits (no exaggeration) trying to miter that large outer border and then center and layer it, especially with the top edged with 324 teen tiny prairie points that faced outward. Eventually, thanks to the shifting nature of fabric, husbandly support, a chocolate or two, the entire mess was wrangled into submission, basted thoroughly, and hand-quilted. The back is not perfect, but looks very good considering the mental and physical effort required. My guess is that most complex backs are not perfect to their makers but look fine to everyone else.