Roy Carin said:

There is more of it if you use IDCLEVxx or -warp.

Some levels are, as you observe, incomplete. In particular in the copy I
have, MAP10 appears to lack an exit line, as do several others.

That's not to say there isn't another exit (fall into an exit damage
sector, kill a boss brain object, etc.) but I didn't check that hard.

I don't know how up to date the following is:

(From http://freedoom.sourceforge.net/status/levels_list)

# status:
#    assigned   -     A level is assigned to someone to work on
#    in dev      -    A beta version (not yet finished) of the level has
#            been submitted and is in the build
#    done      -    Completed level in the build
#    none      -    Level has not yet been assigned to anyone
#
# map    name            status        author
#
MAP01     entryway        done        spaceforce
MAP02    underhalls        done        tarin
MAP03    the gantlet        done         sgtcrispy
MAP04    the focus        done        Macro11_1 2005-12-25
MAP05    the waste tunnels    done        amarande
MAP06    the crusher        done        mystic
MAP07    dead simple        done        tarin
MAP08    tricks and traps    assigned    captain mellow 2005-08-10
MAP09    the pit            assigned    godcells 2005-12-04
MAP10    refueling base        in dev        Archvile64 14/04/02
MAP11    'o' of destruction!    done        kaiser
MAP12     the factory        in dev        rickclark 24/1/02
MAP13    downtown        in dev        lurker 6/10/02
MAP14    the inmost dens        assigned    geekmarine 2005/03/14
MAP15    industrial zone
MAP16    suburbs            done        hyena
MAP17    tenements        assigned    kaiser 2005/03/27
MAP18    the courtyard        done        zigmund
MAP19    the citadel
MAP20    gotcha!            done        lazer
MAP21    nirvana            done        amarande
MAP22    the catacombs        done        tarin
MAP23    barrels o' fun        in dev        submerge 9/11/2002
MAP24    the chasm       
MAP25    bloodfalls        done        cyb
MAP26    the abandoned mines    done        torn
MAP27    monster condo        in dev        bastet 15/9/02
MAP28    the spirit world    assigned    jond 2005/03/12
MAP29    the living end        done        amarande
MAP30    icon of sin        done        Cacodemon_Leader
MAP31    wolfenstein        in dev        oblivion 4/8/02
MAP32    grosse            done        ajapted

Quoting  Roy Carin  <roy_carin_mail-nospam@yahoo.com.au>:

[If you ask on rgcd.playing, read on rgcd.playing?]

Skip forwards. When I looked, some levels were there after that, some were
not, some of the ones that were not were polite enough to be an exit
switch in a room. IIRC.