You have to ask the datfile author which checksums are listed in the datfile.
Including or excluding the header (excluding would be correct)....and then of course you have to know how your files look like at the moment (with or without headers).

It works perfectly if you have
a) a nes file with a nes header
b) turned on nes header support
c) a datfile which lists the files' checksums without header information and size for the headerless data

The tosec datfile looks like if it took the full file for checksum calculation...which means you need exactly the same file (= same header). A NES file looks usually like: a changeable header + unchangeable romdata. So it's not that clever to include the changeable header into the crc32 calculation....




Roman Scherzer