Why are you assuming that buffs from multiple companions stack? It makes more sense that the only buffs that apply are the ones related to the companion you assign the task to. The companion does all the work, not you.
Where is that mentioned, can you quote it? Maybe you got confused with something you read somewhere else?
I just updated the guide! I hope you find the additions useful.
I've put my current thoughts into this (particularly about critical crafting), and I've also added colored text and critical crafting (not gathering or missions) charts at the end of the summaries.
I like the improvements. Btw I think you forgot the add the +2 crit bonus in diplomacy of the trooper Companion or mixed it up with +2 treasure hunting.