I don't know about the missing bitrate, what I usually do if I find a bunch of 'empty bitrates' is look at the size of the file, then compare it to other sizes and see what the bitrate is, usually you can tell that way.
As for the bigger the bitrate the better, I don't think that's true. I personally like 128, sounds good and file is pretty small. I'll go up to 192 if I
HAVE to, but I try not to go higher. When I have gone up into the 200's, I think t hey sound like crap like someone held the microphone up to their speaker almost like the bass and treble aren't there, that's just me though and my set up. I have a sub, 2 highs, and 2 tweaters and I think it sounds (with a 128 or 160) pretty damn close to the system I have in my truck and I got a pretty good system in there.