Oh yeah, I probably should have given you an update too.
Creech said that I'll be fine so long as I don't pre-load my tag with offline achievements and then unlock them when I get back home. I don't even know how to do that, lol. He said "we'll be fine, then." I'll make sure to use SmartGlass and Xbox.com on my phone when I'm away just in case though
I've only had it less than 3 days! I got 325G on the 360, I boot up the X1 and they all pop again. Works both ways provided you own both game digitally! It'd take someone 50hrs minimum to get 600G on the game! The achievements suck!