回複：Many thanks! My main concern is that

It would arouse suspicion and cause unnecessary hassle with an IO upon next entry when they come back in 11+ months if my dad's green card won't scan properly. You see, they have been doing this one-year stay in China thing for a few times now and have so far had no trouble with an IO when they come back. But back on my mind, I'm always afraid they'd be stopped next time. 
-I suggest your parents to get the reentry permit to travel to China if they want to stay there for a longer time. Also, if you worry too much about his green card after MRI, your father may go to the local USCIS office to check it (tell IO what happened).