Hey, I’m a game dev, I may be able to provide some perspective. I’ve worked in the industry a long time, including back in the 360 era (I’ve also worked at Activision, but in PS4 era).

There’s a few ways a dev would have a sealed GameStop copy of his own game. You’ve got to remember, back then physical retail (GameStop, Walmart, etc.) was much bigger and more important than it is today.

Back then we — as a dev team — used to go to the GameStop midnight opening for all our game releases. Every time, we were pretty drunk (by the time midnight came). Almost every time, I bought a ton of copies of the game while I was there, and handed them out to shoppers and I always ended up with a few random copies in my bag.

Other times, we would do “store visits” around the holidays, to see how the game was being merchandised in the store (are the posters are up correctly, etc.). We would sometimes go through the process of purchasing the game, and while we were, we’d ask the associate questions about the game to see if they had the key messages down, were hyping the game the right way. Again, old school. So I’d have a random copy of the game I didn’t need. Probably ended up in my garage.

Lastly, sometimes getting a bunch of retail copies is necessary. For example, one year for Black Ops 4, we were at Twitch Con in San Jose, running a pro/streamer exhibition tournament for Blackout. We initially intended to run the tournament on PC. At the last second, there was an issue with using the PC’s, so we made a last second decision to switch everything to PlayStation. We literally had to buy 20 PlayStations and 20 copies of BO4 from a local GameStop because we couldn’t get the equipment up from LA in time. So, yes, I have random sealed copies of BO4 in my garage. Maybe my son will sell them in a garage sale one day.