The first cohort thing was changed in the 1.2 patch. A first cohort is a cohort with an eagle; that's always been the case, and that's how it worked in history. Originally you could only get them as rewards from the senate, but as of 1.2 you can train them in the city of Rome as long as it has the necessary buildings to produce the regular legionary unit of the same type.

I missed this alteration in my main update for that section of the guide, and I've not managed to get chance to edit it to the new, correct information. Heh; I've not had chance to do a thing with the guide in over a month. It's still stuck midway through its 1.2 update. I do have hope that I'll be able to do something on Friday, when I anticipate getting a day off from this incredibly lousy course I'm on. Grumble, grumble: I left university and ended up at what feels like nursery school. Grumble. So much time wasted!

Sorry for the confusion.