The conversion Otakon Doom (http://www.doomwadstation.net/main/otakon.html ) fails.
1) The marine's head is not replaced by Priss's head
2) The cursor in the level select screen is not replaced.
This works properly in Doom Legacy 1.45 and Chocolate Doom.
This wad is incompatible with the lump namespacing system used by (nearly) all modern engines, a prevalent issue with old vanilla wads using NWT to handle graphics instead of deutex/deusf (the commonly available version of Mordeth E1 has the same problem)
The missing graphics you mention are in otakugfx.wad between S_START and S_END markers, which means they are only recognised as sprite names. Looking them up as patch names fails intentionally - otherwise you get into all sorts of strife, to cite a recent example looking for a patch named BLUMAP and getting a colormap instead.
Would it be possible to have some kind of switch for compatibility mode, that can be used to read old wad files that don't meet newer standards?