how does xbox.com's server handle conflicts if I plug in an older HDD from 3 years ago that has offline achievements when I have the same game played this past year on a newer HDD with online achievements? older HDD has last game played 04/02/2010, newer HDD 10/09/2012. will it merge my data (achievements) or will it erase them since the dates conflict?
Ah, I don't believe it will conflict, or neither will it update, I once corrupted my profile without knowing and signed in, it had 0GS and my GS that was server stored was at 50K+, it didn't update the difference, I don't know if this may be the same but I believe it's a close enough example, but if you were to play the game with the saves from your older HDD if may load and pop the achievements, other than that I'm not entirely sure, and hopefully someone within the community can give you a better answer over mine, but best of luck with this
Once the profile from the old hard drive is taken online it will just update the achievements that may not have been unlocked again on the new hard drive. There will be no conflict as the Microsoft server will just see the update and difference in Gamerscore and merge the profile data. *Hope that makes sence lol*