Please confirm if this is a myth or not

Sources say that the drop is 100% for 1 person in that party. So for example, if 4 people in that dungeon all need that key item, it will drop for 1 person out of the 4 that needs it.

So far, a fc/ls member ran AV and DD, he was the only one that needed the item, he got it 100%
I ran 3 AV's this morning, the last one I did, I was the only one that need the item, and I got it.

I did Quan (hard) I thought I was the only that needed it, I did not get it, but I never asked the group.

Please post the findings you see and happy grinding!