Activity rank : Achievement points calculation

[Najrah]

According to the activity rank, my account has 3245 achievement points. However, according to the armory, just by adding up 3 of my characters' achievement points I have:
2305 + 2215 + 2035 = 6555 achievement points.

Should I assume that some achievements are not counted? If so, which ones?

PS: I had no idea where I should I have put this topic, forgive me if this section is inadequate.

[Remphan]

Points from achievements cannot be duplicated. For example you can have the same achievement completed on 4 characters, but it'll be counted only once. RIP my english

[Najrah]

Oh really? So sad. Thanks