User blog comment:Deathstalker666/The Sound of Shotguns/@comment-1496755-20170308215935/@comment-1496755-20170310082438

It's a full episode replacement - 9 levels. Plus custom music (classical, of course), some custom menu graphics and probably some evil dead shotgun sounds. Map desing is so-so.

So, E12N is 4 maps from this episode thingie (+ custom music from E1M1 to E1M6), plus 5 other maps (4 of which we have already identified). Which means there's 1 more to discover... and it's a pretty evil one :D