Chad,
Here a some UserAgents for which the MatchUserAgent routine couldn't find a matching browser.
Mozilla/4.03 [fr] (Win95; U)
Mozilla/4.05 [fr] (Win95; I)
Mozilla/4.05 [fr]C-SYMPA (Win95; I)
Mozilla/4.5 [fr] (Macintosh; U; PPC)
Mozilla/4.6 [en]C-SYMPA (Win98; U)
Mozilla/4.61 [en] (OS/2; U)
Mozilla/4.7 [fr] (Win98; U)
Mozilla/4.7 [fr] (WinNT; I)
Mozilla/4.7 [fr]C-CCK-MCD videotron (Win95; I)
Mozilla/4.7 [fr]C-NECCK (Win98; U)
Mozilla/4.7 [fr]C-SYMPA (Win95; U)
Mozilla/4.7 [fr]C-SYMPA (Win98; U)
Mozilla/4.7 [fr]C-SYMPA (WinNT; U)
Mozilla/4.75 [en]C-BESI (Windows NT 5.0; U)
Mozilla/4.75 [fr]C-BESI (Windows NT 5.0; U)
Mozilla/4.77 [en]C-CCK-MCD AC20010903 (Win95; U)
Mozilla/5.0 (Macintosh; U; PPC Mac OS X; en) AppleWebKit/74 (KHTML, like Gecko) Safari/74
Mozilla/5.0 (Macintosh; U; PPC Mac OS X; en-us) AppleWebKit/85 (KHTML, like Gecko) Safari/85
Mozilla/5.0 (Macintosh; U; PPC Mac OS X; fr-fr) AppleWebKit/73 (KHTML, like Gecko) Safari/73
Mozilla/5.0 (Macintosh; U; PPC Mac OS X; fr-fr) AppleWebKit/74 (KHTML, like Gecko) Safari/74
Opera/6.04 (Windows 98; U) [en]
Opera/6.06 (Windows 98; U) [fr]
Regards