In the Civilopedia the Shogun-1 -> Shogun-10 descriptions look like they were copy and pasted. The only thing that changes according to the Civilopedia is the Attack and Defence. Lazy lazy lazy :) However in playing the scenario the Shogun also gains other abilities.

I have seen my Shogun "treat all terrain as roads" and I do believe the "sneak attack" ability.

The only way you know your Shogun gets this upgrades is by using him and noticing things have changed. Not a 'bug' persay, but sloppy documentation for sure!

Cheers,

if you want to know the upgrade look in Civilopedia under any Shogun . you will see the words " Shogun upgrade" in blue . click on this and it will show all the upgrades you get with each level