With help of the famous experimental method I found grub4dos internal function cmp can be used for more than blocklists, comparison of whole-sectors or two files with identical filesize.
If comparing a file and a bloklist or two blocklists, cmp seems to take skip and filesize in the same way as known for cat. As far as I know this is undocumented. Please correct me if I am wrong
See first print-screen for an example:
BTW as can be seen even cmp --hex FILE is willing to take skip, but the value of %@retval% seems to have the meaning that cat --hex succeeded to give output on screen - nothing more
As long as filesize is same, normal cmp with skip seems to give correct results. See second print-screen for comparison of a file and a blocklist:
Same for two blocklists, see last print-screen:
BTW as can bee seen even dd seems to take copy-size after the blocklist comma - bs and count does not seem necessary in this case
Used grub4dos version: 2022-12-22