The points you should get when completing an account-wide achievement are not granted to all the character of your account, but only to the one you’ve completed it with, meaning that you can see the points earned in the achievement window, but if you go to the guild roster all the other character will still have the same amount.
This means that if you complete an achiement with an alt, you’ll see the achievement as “completed” on your main too, but you’ll not earn any points from it.
Account wide achievements counts for all characters in the account and add points. Ofc character only point count is different always. Make sure You have checked in your settngs to show Achievements on each character, as there is an setting in which you can hide your sum total of the account on any character you want and it will show only points of that character.
To be honest i’ve always found the guild UI a bit buggy and off with acheivements. The roster currently shows me at 30,010 points, which is a lot less than the 35,725 i actually have. Even Armory and my forum avatar shows them wrong at 35,695.