Veracrypt with multiple keyfiles

[philsmd]

the file checksum is calculated internally by hashcat. All the files are combined to later create the checksum (as veracrypt does too)

Therefore, if you do NOT know which files you used or the order of the files, you need to try each and every one of them in sequence (e.g. in a batch/shell script):
hashcat_cmd1
hashcat_cmd2
hashcat_cmd3
hashcat_cmd4
etc