How do rockstar games handle cross title unlockable content?

The only documented expansion in the source is Red Dead Redemption: Undead Nightmare, which is described as a standalone add‑on that expands the single‑player campaign and adds cosmetic items. No mention is made of any unlockables that are shared between Red Dead Redemption, Undead Nightmare, or other Rockstar titles. Therefore, based on the evidence supplied, Rockstar Games does not appear to implement cross‑title unlockable content, at least not within the context of this expansion. Without additional sources, it is not possible to confirm whether Rockstar has ever employed such a system in other games. A definitive answer would require further evidence from other Rockstar titles or official statements.