i killed a legendary albino deathclaw earlier and all he had on him was deathclaw meat...

Occasionally I kill a legendary that doesn't drop anything. I think it's just a bug though.

It's possible somebody else picked up the weapon. Your companions will do that on occasion. I think nearby NPCs do it too.

ah, ok, i was by myself with no-one else around

rarely they just don't have anything. My theory is thats the missing medic legendaries.

If the legendary have been killed by someone else earlier and weapon taken, legendary spawns again, but this time without any legendary weapons. This ain't sure of, just guessing. I haven't seen any legendary person, creature or thing that doesn't have any legendary item. I know that if npc nearby it happens they take the items.

Cheers,

-klevs