The long, regular and short measurements apply not only to the sleeve length but also to the jacket length. The tailor will measure the jacket length form the nape of the neck to the bottom hem, i.e., down the back from the base of the folded over collar to the bottom hem. From what I have read, the jacket length is to come to the fell of the kilt. If it is longer, it interferes with the motion of the pleats.

To get these measurements to work on a jacket may require some tailoring. For example, I am 6'1" tall. However, I have long legs and a short torso. My sleeve length for a jacket is 26 in. Regular size jackets which come to the fell or ever-so-slightly above it, typically do not have sufficiently long sleeves. If I get a long, the sleeves may be a tad too long, however, the jacket will hang too low below the fell. So, I have a choice, get the regular and have the sleeves let down. Or get a long and have the length taken up and the sleeves shortened a bit. I have done both. The former is easier if there is sufficient fabric in the sleeves and the lining. However, note that if the jacket is vintage, pressing out the old crease may leave a mark. The latter approach is harder to do, but does not require pressing out a crease in a way that will show. The bottom line is, if you want the measurements to work out, have a tailor measure you and then communicate this information to the jacket maker so that the jacket requiring the lease tailoring can be obtained.