in TOSEC it's alike to what Rocknroms suggests:
The TOSEC Naming Convention v1 wrote:* (Disk/File/Tape x of y Side A/B)
This field is used if the game spans more than one disk, or is comprised of
multiple files. When there are 9 or less disks, the format of (Disk 1 of 3)
is used. If there are 10 or more disks, then the entry needs to change to
(Disk 01 of 13) to maintain consistency. In cases where double sided tapes
or disks are involved, the "Side A/B" entry is also included.
Ex: "Legend of TOSEC, The (1986)(DevStudio)(US)(File 1 of 2)"
Ex: "Legend of TOSEC, The (1986)(DevStudio)(US)(File 2 of 2)"
Ex: "Legend of TOSEC, The (1986)(DevStudio)(US)(Side A)"
Ex: "Legend of TOSEC, The (1986)(DevStudio)(US)(Side B)"
Ex: "Legend of TOSEC, The (1986)(DevStudio)(US)(Disk 01 of 11)"
Ex: "Legend of TOSEC, The (1986)(DevStudio)(US)(Disk 08 of 11)"
Ex: "Legend of TOSEC, The (1986)(DevStudio)(US)(Disk 10 of 11)"
Ex: "Legend of TOSEC, The (1986)(DevStudio)(US)(Disk 1 of 2 Side A)"
Ex: "Legend of TOSEC, The (1986)(DevStudio)(US)(Disk 1 of 2 Side B)"
Ex: "Legend of TOSEC, The (1986)(DevStudio)(US)(Disk 2 of 2 Side A)"
Ex: "Legend of TOSEC, The (1986)(DevStudio)(US)(Disk 2 of 2 Side B)"
Ex: "Legend of TOSEC, The (1986)(DevStudio)(US)(Tape 1 of 2 Side A)"
Ex: "Legend of TOSEC, The (1986)(DevStudio)(US)(Tape 1 of 2 Side B)"
Ex: "Legend of TOSEC, The (1986)(DevStudio)(US)(Tape 2 of 2 Side A)"
Ex: "Legend of TOSEC, The (1986)(DevStudio)(US)(Tape 2 of 2 Side B)"
** NOTE: In cases where multi-file zips are used, the parent's zipname should
reflect the contents of the zip.
The files :
"Legend of TOSEC, The (1986)(DevStudio)(US)(Disk 1 of 2).bin"
"Legend of TOSEC, The (1986)(DevStudio)(US)(Disk 2 of 2).bin"
would be included in the zip called:
"Legend of TOSEC, The (1986)(DevStudio)(US)[2 Disks].zip"
* (disk label)
If the disk label is known, this field following the (Disk x of y) entry
should contain it. This is mainly used when save, program, install, or
other custom names might be requested by the game itself. (Disk 2 of 3) is
not useful by itself when the program asks you to "Insert Character Disk".
Ex: "Legend of TOSEC, The (1986)(DevStudio)(US)(Disk 1 of 2)(Program)"
Ex: "Legend of TOSEC, The (1986)(DevStudio)(US)(Disk 2 of 2)(Data)"
Ex: "Legend of TOSEC, The (1986)(DevStudio)(US)(Disk 2 of 2)(Disk B)"
but it makes more sense there, since 1st field always denotes medium from a set - it has a different meanig
here it's only a counter: A, B, C or 0, 1, 2 or I, II, III can be a counters too
so in TOSEC also Enemy Zero would be with labels
(Disc 1)(Disc A) and (Disc 1)(Disc 0) overlap, but (Disc 1) does not express this situation fully, imho,
(Disc 1 of 2)(Disc A) would, as would (Disc A) <- not as complete as previous one though, but that's what we got
also it's the same with (Disc 1 of 4)(Disc 0) and (Disc 0), though 1st is more descriptive again, both are fine, imho