That's a pretty good (and fairly accurate despite it's "breve" nature) overview.
I teach this as part of my class and have some other resources.
When you say "guitar repertoire" you have to realize that music for "guitar" specifically really didn't exist until the Classical Period in standard notation.
Before that it was Lute music, and it was written in tablature (thought rhythmic elements were present in some forms of tablature). Viheuala music might be the closest thing (or possibly, Baroque guitar).
So it depends on how specific you want to be. As Stephen mentions, you might see them in interpretations (transcriptions) of early music not originally for Guitar, or for modern pieces, but outside of that they'd be pretty scarce.
And yes, here in the states we call them "double whole notes".
I've never seen any symbol for anything longer though (IOW, never a "triple whole note").
I suppose you could have a dotted double whole (or double, triple, dotted, etc.) and increase the length a bit, but most likely anything longer than that would simply be tied or and indication like "sustain" or "let ring" etc. might be included.