I couldn't get the quest start item to drop even after many tens of kills, so I looked wowhead comments and found this one to be accurate https://tbc.wowhead.com/item=23759/rune-covered-tablet#comments:id=3344897

After I turned in A Small Start (9506) quest, 3rd kill dropped the quest start item. I did not turn in or accept other quests in between.

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