The differences have to do with the number of pattern components and the way these are used in the doll design.
In two dimensional designs, there are most frequently only two flat surfaces to work with: a front and a back side of the doll. However, some doll patterns like these do include an additional boot. This boot or shoe will be a pattern that is two dimensional as well, having only a front side and a back side. Now given that these patterns have only two sides, it is not correct to assume that your doll will not “look” three dimensional. However, those who have little experience in making dolls will assume this is what it means when the pattern is labeled as such. Dolls always take on a 3D quality when they are stuffed. The proportions of a two dimensional doll pattern are very specific to the eventual appearance of a rag doll. This in turn makes the stuffing of a rag doll, an art form in and of itself. This you will quickly determine on your own after having stuffed a doll incorrectly. Hence, the random affectation from somewhere in the classroom, “Teacher, my doll looks funny.”
A three dimensional pattern eliminates much of the guess work or “experience necessary” when stuffing a doll. These patterns must be constructed in a particular order and the the darts must always be lined up in order for the doll artist to have success with them. This is because the compensation for inexperience comes in the manipulation of components within the design. Neither pattern type is necessarily superior, these are merely options given according to the skills and preferences of those artists using them. In other words, three dimensional doll patterns do not necessarily make more attractive dolls or are not more valuable to doll collectors because of their number of parts.
There are, in fact, many highly valued rag dolls in museum collections that are constructed from simple, two dimensional patterns. I enjoy working with both types of patterns. Students, most usually do not. This is because a three dimensional pattern “looks” more intimidating prior to it’s assembly.