I installed Fire Emblem Echoes long ago, but I have not really played it. Today, I used CIAngel to create a CIAs of the Update (1.1) and the DLC (it downloaded 34 parts), and then install them with FBI (there were no installation errors.) When I checked if DLC had been installed, I too noticed those "dummy" and "content023_es" files that the original poster mentioned.
· Have all DLC maps been already released?
As far as I know, there should be 27 DLC maps, but CIAngel downloaded more parts. In fact, I pretty sure that I have all maps installed and the "dummy" and "content023_es." Unless these are additional data of other (properly titled) maps.
· Is it a faulty installation?
Unfortunately, I cannot test the DLC maps because I have not even started a campaign in FE Echoes.
· Do I need to download a "more recent" DLC, say, from that ISO site?