So (I think) you're talking about two different weapons. Apologies, but it's a little hard to parse out what you're saying. Neither weapon *requires* a lore check to get or use.
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Blighted Village:
you find the blueprints. a check is made to see if you know where to find a particular ingredient... sussur bark. if you failed the check, you don't know where to look for the sussur bark. however, you can still find the bark. tip: it's in the underdark on the sussur tree near the hook horrors.
then you take that sussur bark back to the blighted village forge. you use the forge there and add the sussur bark. next, you add in what type of weapon you want to enchant. it has to be a dagger, sickle, or greatsword. when the process is finished then you have a Sussur dagger, or sickle, or greatsword, depending.
no "lore" check is required to do this.
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Blood of Lathander:
this is an item in the githyanki creche in the monastery.
you probably found some blood encased in amber. all missing the lore check here does is let you know that this is probably a decoy. it's not the real blood of lathander.
to find the real blood of lathander, which is a weapon, you have to turn the statues in that area in particular directions. one statue will get stuck while turning. you can put oil on it to make it turn or you can hit it to make it keep turning. if you choose to hit it, use a pretty strong character to get past its toughness.
that will cause a secret door wall to open. go through that and proceed. at the end of the path, once you get past the traps, you will find the blood of lathander weapon.