DH, KLHM, LBM, LLNS, LSK, NDN, RGN, RZN, TH,...

Supply exactly one missing member - there are a few to choose from.

Items that meet the full restriction of the examples are marked with a +.  Those with the quality not encountered in the examples are marked with a -. The others are like the first two solutions offered, MNTN and HW.

LBM       +
LSK       +
RZN       +
RKNSS     +
CLFRN
CLRD
CNNCTCT
DLWR
FLRD
GRG
HW
DH        +
LLNS      +
NDN       +
W         +
KNSS
KNTCK
LSN
MN
MRLND
MSSCHSTTS
MCHGN
MNNST
MSSSSPP
MSSR
MNTN
NBRSK
NVD
NWHMPSHR  -
NWJRS     -
NWMXC     -
NWRK      -
NRTHCRLN  -
NRTHDKT   -
H         +
KLHM      +
RGN       +
PNNSLVN
RHDSLND   -
STHCRLN   -
STHDKT    -
TNNSS
TXS
TH        +
VRMNT
VRGN
WSHNGTN
WSTVRGN   -
WSCNSN
WMNG

OPEN "xxxxxx.txt" FOR INPUT AS #1
CLS
FOR ct = 1 TO 50
  LINE INPUT #1, l$
  l$ = RTRIM$(LEFT$(l$, 23))
  IF INSTR("AEIOUY", LEFT$(l$, 1)) THEN suf$ = "+":  ELSE suf$ = ""
  IF INSTR(l$, " ") THEN suf$ = suf$ + "-"
  DO
    ix = 0
    FOR i = 1 TO LEN(l$)
      IF INSTR("AEIOUY ", MID$(l$, i, 1)) THEN ix = i: EXIT FOR
    NEXT
    IF ix > 0 THEN
       l$ = LEFT$(l$, ix - 1) + MID$(l$, ix + 1)
    END IF
  LOOP UNTIL ix = 0
  PRINT l$; TAB(11); suf$
  IF ct = 25 THEN DO: LOOP UNTIL INKEY$ > ""
NEXT

File name above is obscured so as not to be a complete give-away.