50 Coins of Ancestry

In WotLK, there is a total of 75 coins of ancestry scattered all around Azeroth and Outland.

It would be kinda easy for a lvl 80 to get two thirds of the coins with decent footwork.

This will be a lot harder with the lvl75 and 80 elite guards added to the capital cities. (May require being at lvl 80 if you don't have stealth)
Also well worth it to buy 400 Festival Dumplings: http://wotlk.wowhead.com/?item=21537 Fastest mana recharge in the game when taken with water.
Last year, I failed to get the one from Stratholme, but now I have a key..

It's not necessarily a bug; the system just can't tell that you previously had those coins. It doesn't run on magic. The few retroactive achievements work by either noting your possession of an object that 'proves' you had it complete, like my clockwork rocket bot. Because I have that toy from last year's Winter's Veil, I retroactively got the 'open a present' achievement. They also work by noting your personal completed quests, which is why I have a few 'slay this boss' retroactive achievements, and not others that I clearly remember laying low.