Probably because there is no such thing as an "official" spec. Try as we might to source accurate data (via Wookiepedia or elsewhere), converting that data into a gaming format is another matter. Then, there's also the issue of scale... if everything adheres to Shields = Length x2, Armor = Length x1.5, and Systems = Length x1... then balancing weapons efficacy needs to be taken into account. For instance, a handful of starfighters and auxiliary bombers can rip apart a Star Destroyer in the movies, but in our games, an ISDs shields make it de facto impervious to small craft (unless massive and sustained warhead attacks are used). So, there's the issue of making sure starfighters get their due without compromising the strength of capital ships as well. At the end of the day, it really doesn't matter what the final Length multiplier is going to be. We could make the ISD's Shields 8000, but this means we'd have to make sure weapon damage goes up to accommodate for this relativistic increase. My rule of thumb is to give a Laser Cannon a damage value of 1. This is the simplest baseline we can start with, and it allows us to scale up from there. Another thumb rule is that an ISD should be able to incapacitate a CORV in a single round.
