... or an exercise in branding intended to boost sales? I call shenanigans: http://www.mobygames.com/game/dos/daryl-f-gates-police-quest-open-season/cover-art/gameCoverId,148791/

Amazon seems to think so (1 2 3). Wikipedia's less convinced ("Daryl F. Gates' Police Quest: Open Season is the fourth installment of Sierra Entertainment's popular Police Quest computer game series. [...] The game is listed as Police Quest 4 (PQ4) in the manual. It is also shown in the file names and the credits, and when exiting the game in DOS, "Thank you for playing Police Quest IV: Open Season".") Abandonia even less so.

Tagged-line title it is then.

The grammarian in me finds the current title an unstable compromise between Wikipedia's (put in the darned apostrophe already!) and the short version.

Based on the screens, in the opening it's called simply Open Season, and in the main menu it's just Police Quest. I would leave it as it is now.

Tag-lined title: Can't make up make their mind for a dang title, it is then. :p