No weekly elite mark credit for killing Naul

Time: 5:40 Server time
Frequency: once
World name: Cactuar
Character name: Aliera Nariel
NPC name:
Monster name: Naul
Class/Level: MNK 50
Party or solo: Solo
Area and coordinates: Coerthas highlands (28,8)
Steps:
1. Heard Naul had spawned, ran to the spawn point with 50+ other adventurers
2. Fought Naul because someone else had pulled, got off a Shoulder Tackle and a Howling Fist before he died.
3. Received the following rewards for killing him:
You have been rewarded for your contribution in slaying the mark.
You obtain 1 Allied Seal.
You obtain 3 Allagan tomestones of mythology.
4. Noticed I didn't get the 20 seals for the weekly Elite Mark I have in my key items, opened inventory and saw that it was still there, the portrait hasn't X'd out, nor has it disappeared like the daily Marks do

I've killed him two times but didn't get the credit cause there were too many there so I couldn't deal enough damage.
That's the problem you need to deal more damage to get credited, which is impossible when there are so many others there too