Today around 4AM Central time US I completed the raid "Crota's End" on hard difficulty for the VERY FIRST time on my TITAN. The previous day I completed the raid twice in the same day on my HUNTER and WARLOCK. I received the GLOWHOO shader for my HUNTER and WARLOCK for completing the FIRST time. I placed the GLOWHOO shader that was on my HUNTER into the VAULT after deciding I wanted to see what the GLOWHOO shader looked like on my TITAN and when I completed the "Crota's End" raid on hard mode difficulty on my TITAN I did no receive the GLOWHOO shader even though It was my first hard mode difficulty "Crota's End" completion around 4AM Central US time. I do not know if this is intended or a bug but as I recall the GLOWHOO shader was rewarded for completion the "Crota's End" hard mode difficulty raid for the first time and I had not received it on my TITAN'S FIRST completion. My inventory was NOT FULL and I had at least ONE slot open.
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I don't think you're guaranteed anything. There were times I didn't get Chatterwhite even when I didn't have it on me, and times when I did when I did have it. RNG.