I seem to recall older versions of RedHat started the human users at 100 and put service users from 50. The differences in setup to do that might give you some ideas of comparison. I don't know how far back you would want to go to find a version that still does that, though. You might have to go back before they picked up the LSB, which might be quite a ways back.
And then there's the issue of successfully NIS from Linux to Solaris. I know it doesn't work with FreeBSD and Linux: they put some files in different places and for some reason that breaks it.
Wade.