The Yarn Harlot's recent post about the ribbing not matching up on the back and front pieces of a sweater reminded me of something I've always wondered about published patterns: how many sizes are actually test knitted?
I think it must be incredibly difficult to knit one sample, in one size, and extrapolate to even one other size, never mind half a dozen different sizes. Don't get me wrong, no one respects math more than I do. I know scaling up or down is mostly a matter of math. However, as the Yarn Harlot has demonstrated, and as I've noticed in more than one commercial pattern, merely adding or subtracting stitches isn't the way to go! In the Yarn Harlot's case, obviously better tech or pattern editing would have caught the mistake. (And you would think, since this was a Rowan pattern, they'd have been on the ball here!) And a good pattern editor goes a long, long way towards making a pattern both easy to decipher and technically correct.
However, I firmly believe that the devil is in the details. I think even if you carefully match up the pattern repeats at the shoulders and side seams for every single size, there's always going to be some issue with, say, the armscye decreases not being symmetric with the lace repeats, or the hem ribbing isn't centred around the cable motifs. Basically, I think there's a whole bunch of details that you wouldn't even think would be a problem until you actually knit the damn thing, in all the sizes.
I don't know how many pattern publishers actually knit every pattern in every size. It would be incredibly time-consuming, and therefore expensive, I would think. So I generally check for errata and I google extensively before I start a project. (I won't live long enough to make all my own mistakes, so I may as well learn from others'!)
The Limey had a great idea a little while ago: a knitting simulator. You'd give it a pattern, and the computer would simulate how the finished piece would look. So you'd get to see, for instance, how your 2x2 ribbing will flow into your lace or cable pattern. Or how your pattern repeats will look where the body meets the sleeves at the seams. Or exactly how deep that v-neck is going to be.
Is there already a computer program that does this? I'm pretty sure not, as it would be incredibly difficult to write, I would think. But wouldn't it be great if it existed? The Harlot's ribbing would totally have matched at the seam then!