All Nippon shafts come in discrete lengths, meaning the manufacturer pre-trims the tip end, but leaves the butt end ~ 1" to 1.5" over standard length. They do this so club-builders can customize the length as needed and avoid using an extension for most builds. If you are working with a club-builder, they will know how to measure and trim the butt end of the shaft during installation to achieve the desired final playing length. If you are trimming yourself and need instructions, please let us know so we can help.
Nippon iron shafts never need to be tip trimmed. Butt trimming is only needed to achieve final desired playing length (which includes the head and grip).
The most important thing for you to do is to select the iron shaft needed for your club# (ie. 3-iron, 5-iron, PW.. ). If the iron shaft you need is not available or in stock, it is generally acceptable to use the shaft for the next adjacent iron club.
Nippon shafts are unique in that both 0.355" tip and 0.370" tip shafts come in discrete lengths. Most shaft manufacturers only offer 0.355" tip shafts in discrete lengths.