I think part of the problem is Janome at some point made a version of the existing 130 / 705 system, and just kept insisting it is a 130 neelde (or HAx1, 15x1). Organ needles are just ever so slighly shorter (if I remember correctly), than the standard set for this system. Most models by far isn't affected by this slight difference, but it's consisitent, and some report it makes a big difference for their machine.
I looked it up, and I find conflicting info on the SP letter designation? I guess Schmentz' homepages are to be trusted though. Some info list it as sharp point? I guess there are various needle tips available for overlockers, since we sew all kinds of fabrics on them.
Surest1tch; good of you to remember, I would not order from him. There are others. I received a sealed package of Schmetz needles, flawless condition, and I have to admit, it was probably from a different seller then. I just remeber the shops name for some reason.