I was wondering why my Halo Reach Legacy only shows that i beat Halo 3 on Normal when i have beaten it on Legendary…Also on Bungie.net it says ive only completed it on Normal but yet i have the achievment and the Last attachment for the CQB helmet.
you need to do all the levels solo OR co-op for it to regonise it a mix ‘doesn’t count’
I also completed the ODST campaign in its entirety on legendary yet it still doesn’t show up on my legacy either… I know its not much of a big deal but its nice for people to know that I have stayed loyal to all the halo games 
check my game progress for ODST: II Holoe II