I've never had one in my possession, so I'm not surprised. Much of the CPU detection routines were from a 3rd-party library, and the rest (20%) were written by me based on the hardware I have/had available.
If you're willing to ship me a 486dx-120 system I would be happy to debug the code
but for now, just use the -s option to skip the CPU detection and then write in the proper values when you edit the entry. (And I'd be curious to see that entry, since the only 120MHz entry in the database is an AMD x586 CPU -- is that what you have? That reminds me, I never benchmarked my own Pentium 120... I'll have to pull that out and add it to the database. Uses a 60Mhz bus instead of 66MHz...)