TFCK "full length" kilt?

[cessna152towser]

I've been wondering how the length of the kilt got set at "Knee length. More than an inch either way and it isn't a kilt."

I don't think anybody set any rule that a kilt has to be knee length to qualify as a kilt. What I said earlier was simply that this appeared to me to be the public perception.
For those of us who are more interested in kilts we would interpret a kilt as a garment having overlapping front aprons.
Thus while most of us would accept the TFCK long kilt as being a kilt, the average person whom the wearer would meet in the street would see it as a skirt.
On the contrary, my box pleat camo skirt and denim cargo skirt have both been favourably commented on as kilts.
I wear them as casual kilts.
You know, I know, and the manufacturer knows these garments are not kilts because they lack the overlapping front aprons. Indeed the manufacturer (Midas Clothing) specifically differentiates their range as kilts (overlapping front apron) and skirts for men (garments which look superficially similar to a kilt but have no overlapping front apron).
However the person in the street sees a man in a knee length unbifurcated garment and perceives it as a kilt.