It's the stress placed on folding that is the issue. Creases the fabrics, moves the batting. Typically what you want to do if you have to seam two lengths of fabric is you first cut them into two equal pieces. Then you cut one in half the long way and seam it with two seams. So you have 1/4 - 1/2 - 1/4.
You don't have to be far off from center, couple of inches is all you need. Happens for mine with the border print I'll pretty much be dead on. But it's a use quilt and not really a treasure and the print made me happy when I found it. Back in the early 80s I had a number of dresses made of the same sort of material with the border print along a full shirt waist dress, typically it would have the print on half the top too but not always. You can see the huge selvedge still attached, I'll be trimming it down but I used the registration marks in the selvedge to keep the design consistent in addition to pinning every two inches or so.
In the second border print top, the one with the daisies, the seam is a couple inches off of center but within the same "scatter" of the daisies.
Ideally I like the extra wide fabrics but I've been quilting a long time and they weren't always readily available, plus I'm cheap! Most of my backs are large wild prints I get at thrift stores, happens I like large wild prints so that's good. Also marked-down fabric on sale. I've used sheets but they can be heavier than I want, so I've been seaming backs for a long time. Typically they hold up just fine.
Keep in mind that rules are meant to be broken and quilting can be sort of a thrifty hobby, or at least we can make due with what we have when that is all we have. In this case for this quilt I will use the center seam and the less-than-ideal cotton poly blend because it still makes me smile
