Replying to Ski measurement convention?

I understand that there are a few ways to measure the size of a ski, tip to tail, effective edge and base length being the most popular. Although when Ive bought skis online in the past (since I live in the UK), I have been unable to establish how different companies measure the size of their skis. A couple years ago my friend and I bought a pair of Line TC's and Chronics for ourselves, both advertised as 171cm yet when we put them next to each other we noticed a significant size difference and decided to measure them from tip to tail. The Chronics were -2cm and the TC's +2cm of the advertised ski length.

I'm curious to find out whether anyone has any knowledge on how and why ski companies measure their skis differently. Ski companies already give us information on the width of the ski at various lengths of the ski, maybe they should also advertise effective edge, base length and tip & tail length, any thoughts Nsers?