For your example, I think the most complete series title should be used.
"Sangokushi Eiketsuden Series - Sangokushi Eiketsuden" should be used? It's stupid. It's the same thing as the genre and, again, even Tactical Espionage Action is omitted (which is everywhere on the covers and ingame) and in this case it's only the front cover.
I think there's a huge difference between the publisher series (groups different games/releases into the same release series with the same package appearance) and the game/title series (my example falls there, J. B. Harold Series falls there, http://redump.org/disc/33518/ - this one falls there, etc.) which should be treated the same way as genre and moved into the comments.