The premise is interesting but a little unintuitive. As I understand it, an L-seam is defined by having to attach a square by two edges at a time (i.e. two of its sides already have adjacent pieces in the finished part). Consequently, it's order dependent: any sized quilt can have L-seams if you construct a L-shaped piece that needs a corner filled in, even if there is an optimal way. It follows that not every "seam that ends in the middle of the piece" is an L-seam: both ends could have been edges at the time of construction.

As an engineer with no sewing experience, I don't understand why you wouldn't sew one straight edge from the outside in, then sew the other and meet at the corner, avoiding L-turning issues. Please enlighten me.