Just to be clear, the *.rar is always the first in the set that includes *.r00, *.r01 etc, regardless of the upload order. File headers are spread across volumes, but always serially - files packed in early volumes will not have file headers in later volumes. So what you see in the .r00 depends entirely on how large the packed files are.
For reasons explained, this does not help at all if the archive only contains *one* file spread across all the volumes which is itself a RAR that contains passworded files. All that the file headers in the different volumes will tell you is that they contain a single RAR that isn't itself encrypted. What we're interested in is the contents of *that* RAR, and that info can only be in the first *.rar volume, where its contents actually start ... if that's missing, or if the packed RAR is compressed, you're out of luck.
If you want to see what I mean, try downloading
this NZB and try inspecting each volume with
this PHP class or the like, or a hex editor if you know how to read the
RAR specification. Compare the contents of the .rar that Alt.Binz needs to create by PAR2 repair *after downloading all the volumes* (see the small PAR2 to confirm that the .rar is needed) with the .r00 that's actually included in the NZB.
And no, opening a volume in WinRAR or similar doesn't give an accurate view of what's actually in each volume, as those proggies inspect all the volumes in the same directory and collate their file headers.