At a guess, you're running with tradspool. Due to unclean shutdown, overview is substantially out of date with respect to spool content and active file. Renumbering on startup has done its best effort by finding overview stuff, which lags active and spool content, and renumbered active on that basis...which is just plain wrong.
(訳) 起動時に、 「overview が古くなってしまっているので記事の番号を付直」 してくれるのが、悪い方に働いているかと思う

Aug 27 19:04:49 komekome innd: 
tradspool: could not open 
/usr/local/news/spool/articles/comp/cad/231 File exists

comp.cad 0000000231 0000000174 y

news@komekome  20:29:09/010827(~)> ls -l spool/articles/comp/cad/23?
-rw-rw-r--  1 news  mail  4711 Aug 27 09:52 spool/articles/comp/cad/230
-rw-rw-r--  3 news  mail  1750 Aug 18 03:49 spool/articles/comp/cad/231
-rw-rw-r--  1 news  mail   736 Aug 18 08:51 spool/articles/comp/cad/234
-rw-rw-r--  1 news  mail  2736 Aug 20 04:30 spool/articles/comp/cad/237

• 231 は既に使われている。
• 231 よりも大きい数字の譜がある

＠ 内蔵 10G:

7 partitions:
#        size    offset     fstype  
 a:   1433600  12289544     4.2BSD  
 b:   1222656  13723144       swap  
 c:  20066251         0     unused  
 d:   2048000      1544        HFS  1G  MacOS 9.1
 e:  10240000   2049544        HFS  5G  MacOS X
 f:       451  20065800    unknown  
 g:   5120000  14945800     4.2BSD  

＠ 追加 20G:

8 partitions:
#        size    offset     fstype  
 a:    263088         0     4.2BSD  /
 b:    262080    263088       swap  
 c:  39851760         0     unused  
 d:  10239264    525168     4.2BSD  /usr
 e:   6144163  10764432     4.2BSD  
 f:   6144163  23051952     4.2BSD  
 g:  10480544  29196115     4.2BSD  /e