What's the difference between count, num, offset and also others numbering variable (if there is)

[zajimumaaa]

What's the difference between count, num, offset and also others numbering variable (if there is) ?

I notice count is appear in -K option and metadata output, num is appear in the -K options, and offset is appear in archive-format docs but not appear anywhere else.

I want to use the variable as both filename format and archive format. I'm planning to do [date]_[post_id]_[sequence]_[type].[ext] but not sure what to use for the sequence. I want the sequence that persist whether I'm downloading all of post content (like attachment) or just the post image