Nope, I'm actually using the SIGIL.WAD from 1.1 and the 1.2 WIP for testing...
Had to use a Win 10 MD5 summer on my main rig, as trying to run "md5sum" on the 486 got me the error "Program is too big to fit into memory"
(obviously a base mem error)
Anyhoo - I've highlighted the two wad files I'm actually using on this screen grab (also the MD5s for the compat.wads for reference)
https://imgur.com/a/A1nMmUc
For testing if I use the original SIGIL.WAD it will load DOOM 1.9 and SIGIL.WAD and shows the Ultimate DOOM title screen...but just bugs out when I select New Game with the "ERROR: W_GetNumForName: M_EP15 not found!"
In contrast, with SIGIL_COMPAT.WAD - it will show the SIGIL title screen...then bug out at new game again (this is just for comparison)
If I load SIGIL_COMPAT.WAD the classic way - the game works fine - but obviously without 5 episodes...