I think, though haven't confirmed it yet, that you have to build an archery range for the list to show any archer units. I seem to recall running into exactly the same thing, but then once I built the archery range they showed up.

Personally I think it should be handled like when you don't have the resources. You get a "disabled" icon and clicking on it will show you what building(s) you need to actually build it.

Ok, yes that's it.  I built an archery range and then a unit with a bow showed up in the train window.

Also note that you cannot Upgrade an existing unit as they do not get put on the list. Creation of a new Unit does work. Example, select Peon, hit upgrade, the add items, then Save. New Unit name comes up, hit Save again. Nada added to the the Unit list.

This was very doable in the last Beta version.