I have just completed halo 2 A on legendary and didnt unlock the legendary anniversary achivment. No 0x skulls and did get “the grate journey” achivment. Also It did unlock just the normal achivment,but it said on the game menu I finished on legendary.
Even more a wierd it didn’t show the ending with commander Locke
Looking at your service record, you have only completed the mission Regret on normal difficulty, which is why only the achievement for completion on normal has unlocked. Try doing it again on Legendary and seeing if that works.
I have completed Halo 4 on legendary and it took A COUPLE HOURS to unlock the achievements and the service records online are not working properly because it does not show things correct.
Sorry took me a while to reply 
finished regret and got the achivment straight away,thanks alot