The css0.dat file stores information about the scenarios. I have only inspected the file that I have so I can only presume that all files use the same codes. In original RCT, the file was named sc.idx.
The file is RLE compressed and contains a checksum. The version number corresponding to the SV4 file is used for the checksum. The file is encrypted by adding 39393939 and then rotating each DWord right 5 bits.
0000..7FFF : 128 entries of 16 bytes each. Contains the name of
the scenario file in the directory.
0800..27FF : 128 entries of 64 bytes each. Contains the name of the scenario.
2800..29FF : 128 entries of DWords for the company value (dollars multiplied by ten). 80000000 for "not won"
2A00..39FF : 128 entries of 32 bytes each. The name of the winner.
3A00 : Number of scenarios
3A01 : Flag: usu 0; purpose unknown.
3A02,3 : part of creation time of css1.dat file on your computer - second word if original RCT or AA/CF, third word if LL.
3A04..3A07 : low DWord of sum of FileSize of all SC4 files in scenarios directory.
3A08..3A0B : high DWord of sum of FileSize of all SC4 files in scenarios directory.
3A0C..3A1B : 128 bit flags. A bit is reset whenever the scenario becomes available. In original RCT, there were only 32 bits of flags - the remaining 12 bytes are not present.
There is also a checksum for the last scenario availability flags. it is stored as a DWord at 2CA7 (this is in the area for the name of the winner of the MegaPark scenario - since it is a "have fun" scenario, it should not have a name entered.