Sew Be It, I had a nightmare using the commercial 10" batik squares for a pattern. I was supposed to get a number of sub cuts with no waste but the last one was always off. I wrote the company and they indicated that the block sizes could be off because they were hand cut. Now I measure them using a square ruler to see what the real measurement is. (I rarely use precuts because I have to wash the fabric but that is another story).
Mary Ellen Hopkins frequently said that we all have our own personal measurements and if our blocks were not all the same size to measure the smallest one and trim the rest - that works as long as you are not going to show the quilt. Had to follow that advice when I made too many blocks too late at night - sigh.