I had a kit that advertised 3 different sizes: crib, twin and queen. I was making the twin size, and ran out of the contrasting fabric. If I didn't have enough to make a twin-size quilt, heaven help anyone wanting to make the queen-size quilt! And I wasn't short by just a few inches, either: the pattern called for the inner border to be made with that fabric, which also appeared in each block. I had enough for the sides of the border, but not the top.
Fortunately, I was able to buy a "close-enough" match and am making the entire inner border out of it. But the experience taught me not to trust kits again. (I'm a new quilter, and was overwhelmed by all of the decisions you have to make re color, design, amount of fabric to buy, etc. I thought buying a kit would let me just start, if you know what I mean!)