So, when you export a design into an SVG file, you end up with a polygon for each object that intersects the workplane. The polygon is described in the resulting SVG file as a set of coordinates for vertices. For instance, a very simple shape might end up looking like
<path d="M 40 40 L 60 40 L 60 60 L 40 60 L 40 40
which draws a square from (40,40) to (60,40) to (60,60) to (40,60) and back to (40,40). In this case, the square starts at the (40,40) vertex, but I could draw the same square starting at any of the other vertices.
How does Tinkercad choose which vertex to start with? I thought at first that it might be something like "the one closest to the upper left corner", or "the one with the lowest Y value, resolving ties by the lowest X value", or something of the sort, and it would be convenient for a project I'm working on if it worked that way, but it doesn't appear to be consistent in my trials: Sometimes it starts in the upper left, sometimes the lower right, etc.