Most sewing practice with knits calls for a 3/8" seam allowance where the sewer is required to cut 1/8" off the pattern perfectly all the way through. In some cases 1/8" at the sew line is half or even closer to the difference in an entire size.
We do things differently. We use 1/4" seam allowances and don't cut any additional fabric during sewing-removing the room for error relying on each sewer to perfectly cut 1/8".
Additionally, we use the highest quality thread. We can't even buy commercial spools of this stuff. It's very expensive, but is worth the added cost.