If one wants a block to end up a particular size, there are more factors that just the seam allowance that influence that.
Cut size of component pieces - depending on whether one is using die-cut pieces, how one measures - the way I cut around a ruler - makes my pieces a thread or two wider than the ruler. It might be interesting to measure - with a very accurate ruler - just how close one is to the "expected" size. I do not have a die cutter, so am not familiar with how "exact" the dimensions are of a shape that it would cut.
Thread thickness
Seam allowance
Pressing techniques - one can stretch a block quite a bit by ironing it like one was rolling out pie dough - not recommended -
Most patterns available now are designed with a "scant" 1/4 inch seam or "regular" 1/4 inch seam.
There are several videos available showing how to "test for accurate seams in quilting" -
So - does it matter?
I have purchased fabric from a LQS that frayed like crazy. It was very coarsely woven - and I would not buy anything similar to it again. It was a "brand" name, too - but I don't recall whiat.