If you were hoping that you wouldn’t need your Call of Duty: Infinite Warfare disc anymore to play Modern Warfare Remastered when you purchased your retail Legacy edition then that sadly isn’t the case, at least according to the response of Activision Support to one user as well as the remaster’s FAQ.
Asked whether the digital version of Modern Warfare Remastered, which comes with the Legacy edition of IW, worked without the IW disc, Activision Support responsed by saying that the “existing Legacy Edition of IW will remain unchanged. You’ll need your IW disc to play MWR.”
The Modern Warfare Remastered FAQ also states:
For disc-based (physical) Legacy and Legacy Pro Editions of Infinite Warfare on PlayStation 4, Call of Duty: Modern Warfare Remastered is a full game digital download that is redeemed with a voucher code in the box. An internet connection is required to download content. The game disc must be inserted to play Modern Warfare Remastered.
For Digital Legacy and Digital Deluxe Editions of Infinite Warfare on PS4, there is no game disc or voucher code. An internet connection is required to download content. Modern Warfare Remastered and Infinite Warfare are two separate downloads and there is no requirement to have both installed in order to play either piece of content. No game disc is required if you purchased the Digital Legacy or Digital Deluxe Edition of Infinite Warfare.
It looks as if copies of Modern Warfare Remastered that come from physical retail boxes of Infinite Warfare still need the disc even if the remaster is completely digital while the Digital Legacy and Digital Deluxe editions of Infinite Warfare won’t need a disc (because they don’t come with any) to play Modern Warfare Remastered.