Bob's nickname was “Elvis,” a 'reference to' the way he styled his hair. [=people called Bob “Elvis” because he styled his hair in the same way Elvis Presley did]
The course covers ancient history 'with' special 'reference to' the Roman Empire. [=the course is about ancient history and especially about the Roman Empire]
I have something further to add 'with reference to' [='with respect to', 'in regard to'] what was said earlier.
(..) - Sherlock, dear. This taxi driver... Mrs Hudson, isn't it time for your evening soother? Get vehicles, get a helicopter. This phone battery won't last for ever. We'll just have a map reference, not a name. It's a start! Sherlock... Narrows it down from just anyone in London. (..)2010 TvShow: Sherlock Title: A Study in Pink Season: 1 Episode 1