I once bought a template set - actually it was pattern pieces printed on plastic - and then I was to cut them out - so I assumed that the pieces would fit together.
It was after my first king-sized quilt that I measured the square that never seemed to fit right - and it was 1/8 inch longer in one direction than the other. Which explained why it went together nicely in one direction and it was a battle in the other.
After that, I learned to never assume that the measurements were accurate - in patterns or rulers.
I have heard that pre-cuts vary from very accurate to not . I do not buy them because I am in the wash-before-cutting group and it is important to me to get the shrinkage out of the way before proceeding. Or to find out if I have a bleeder.
I just found another piece that I did not get all the excess dye out of before proceeding. Ah, well. One continues to learn and live! I got color transfer to my pressing cloth while I was fusing some interfacing.
I did buy some cut strips at a yard sale once - they were all a full 2-1/2 inches before I washed them. Most of them were about 2-3/8 inches wide after being washed. A Hoffman or Kaufman was one of the brands that shrank. They did not fray because I handled them carefully.